Tuesday, February 09, 2021

adidas ULTRABOOST 21 Multi Tester Review

Article by Jeff Beck, Ivan Luca Corda and Sam Winebaum

adidas Ultraboost 21 ($180)


Sam: Boost oh my, lots of Boost. Back in 2013 the original Energy Boost trainer followed by the adios Boost racer were truly revolutionary as they were introduced with midsoles made of expanded TPU pellets instead of the usual EVA foam. Bouncy, decently forgiving these shoes are among my all time favorites and came after literally decades of stagnant firm EVA foams. 

Boost was well tamed and made performant at the highest levels of competition and by everyday runners by some EVA and some Torsion plastic in the mix and was quite dominate in top level racing until the carbon plated Vaporfly with its far far lighter and energetic PEBA ZoomX foam came on the scene in 2017.

In the meantime, adidas discovered Ultraboost (lots of Boost basically) , and even in its first edition resolutely focused on a soft and flexible ride and knit uppers. UB1 was literally un runnable for me due to their softness and overly flexible forefoot and highly constrictive knit uppers which adidas then struggled to contain with plastic cages. But oh so comfy. adidas found fortune in the shoe as a lifestyle shoe and came out with heavier and heavier other Boost based actual run trainers as almost an afterthought with only the Boston a fine contender.

That is until 2020 when adi shocked us with the adios Pro, a non Boost, carbon rods powered marvel that has proven to contend very well indeed against the Nikes at the top of podiums and for the more recreational racer such as me. 

And then with great fanfare the Ultraboost 21 arrived, a sleek and superb looking monster of a Boost shoe with more regular old and heavy Boost, an extensive new plastic LEP propulsion system and associated pronounced rocker, a colorful and extensive mostly crystal rubber outsole and of course a spectacular upper made with more than 50% recycled ocean plastics in collaboration with Parley’s for the Oceans. All the buttons were being pushed: spectacular  design, a powerful sustainability story, lots of tech visible under foot and up top, and even a now common rocker based geometry. 

At what cost though? Weight for one at 12.7 oz / 360g  (US9) and not a change but still with a $180 price tag. Neither on the surface were show stoppers as weight if fast paces are not the goal doesn’t always make or break a ride and price-well there is a lot of tech, premium materials, and spectacular design in the mix. When adidas offered RTR test pairs for this review I was on board. 


Jeff: Since its introduction in 2015, the adidas Ultraboost has lived in the place between “big cushioned plush daily trainer” and “comfortable lifestyle shoe”. It was adidas’ first running shoe with an all-Boost midsole, and while it gained lots of traction in non-running circles , I found it lacking in the running department. 

The Ultraboost 19 added more cushioning to the forefoot, and a little to the heel, and cleaned up some of the issues with the plastic cage in the upper, with the Ultraboost 20 mostly looking like a colorway update. Then came this shoe - the Ultraboost 21. The biggest departure yet, every element of the shoe has changed, with a redesigned midsole, outsole, and upper, with big changes at every turn. But the most important question, “did it become a better running shoe?”, is a lot more nuanced.


I’ve always had a soft spot for the Adidas Boost line-up and recall my first Energy Boost with great joy. At that time many running stores here in Denmark were hesitant to take the revolutionary Energy Boost into their range. The new and "lively" Boost material did not work well with the traditional view that the midsole's main purpose was to create shock absorption and stability and the focus was not yet really on "energy return”. However, it soon became clear to everyone that the effect of this new type of foam changed an entire industry - within the lifestyle, training and not least the racing category. Turning the clock forward to 2021, and after years of upgrades and great success with several Boost line-ups, it will be exciting to take a closer look at which direction Adidas has gone with the latest version in the range...the Adidas Ultraboost 21.


Jeff/Sam/Ivan Soft upper made of recycled ocean plastics

Sam/Ivan: Beautiful design

Sam/Ivan: A shoe (heavy) that is ideal for slow no agenda shorter runs. Stable, well cushioned, easy to transition. Ideal for heel strikers

Jeff/Sam: Midsole cushioning went up, platform got wider and more supportive

Sam/Ivan: LEP “new torsion” and rocker is effective at slower paces and walking.

Massively cushioned without being mushy or over firm


Jeff/Ivan/Sam:  Tipping the scale over 12.4 oz in a US9 and 14 oz in US11, it’s the heaviest road running shoe we’ve ever worn

Ivan/Sam:  Not the most versatile shoe out there. Best at those shorter and easier runs.


Plastic forefoot plate creates a hoof like “clop clop” with every foot strike, accentuating an awkward stride

Midsole density went up, making the ride firmer and less dynamic

Plastic cage is back, and no extra eyelet to combat heel slip issues

Toebox is sneaky tight with the toe bumper complicating matters

Massive uptick in heel cushioning is lost on those who don’t land on their heels


Beautiful, low front “silhouette” with its low toe bumper and nicely stretchy toe box knit is a touch too low

Ponderously heavy when the pace picks up. Keep ‘em for the slow and easy

Weight and price, limited pace and distance versatile make them, at $180, a mediocre value as a pure running shoe

Ivan: Feels a bit firmer to me than its predecessor despite the “softer” look


Estimated Weight: men's 12.7 oz / 360g  (US9)  /  women's / (US8)

  Samples: men’s 12.4 oz / 352g (US8.5) 14.1 oz / 397g (US11)

Official Stack Height: 30.5 mm / forefoot 20.5 mm

Estimated Full Stack Height: 39mm  heel / 29m forefoot

Available Feb. 2021. $180 

First Impressions and Fit


Jeff:  The Ultraboost 21 is a visually striking shoe, with proportions that resemble a concept shoe. Big curves, outlandish looks, these kinds of shoes usually dry up before they make the jump from the page. The most striking thing, once they were on my foot, was how much wider the forefoot is from last year’s model. Looking straight down at the shoe, the upper is about the same width as the UB20, but the midsole expands out from there, creating a very stable platform. I’m normally a 10.5, but adidas didn’t have any of those for review, so I went up to 11. Fitwise the 11 is actually great for my foot, giving effectively a thumb’s width in front of my big toe - which is how most other brands’ 10.5 fits my foot, so you may want to think about going up a half size.

Sam: It goes without saying the design is spectacular, or at least I think so. From the giant heel area into which the foot nests below the Boost leading to a visual effect of a low silhouette front of the shoe to the bright rear clip which slims as it goes forward, to a sleek streamlined upper highlighted by the contrast of yellow Primeknit + toe mesh outset with off while, to the multi color outsole the  visual design of the Ultraboost 21 conveys a powerful sense of forward motion. 

The fit is true to size for me with a variety of socks. I often struggle with compressive knit uppers over my big toes and for sure did in the original UB but here the front knit is very soft with an easy stretch. The extended toe bumper is quite pliable but low to create the sleek silhouette and I assume also to lock the foot in the broad toe box. All in all it works decently  for my intended uses, shorter slow runs and more casual wear. 

This said I wish the toe bumper was slightly higher for a bit more overhead room. Ok, I understand, the swooping forward from the heel heights to the low appearing front might not look quite as smashing and fast.

The rear hold is superb and the plastic cage of 3 adi stripes was barely noticed, an improvement over some prior caged adidas. 

Ivan: At first glance, I personally think the new Ultraboost 21 looks amazing. Especially the quite oversized looking Boost heel creates a cool look.  I immediately just wanted to jump right into it and feel if it was really as soft and bouncy as it looked. This model, like so many others today, has a close-fitting knit upper that requires a bit of work when getting into the shoe even though the knit is stretchy. However, the high heel cup helps in that regard and then it fits really comfortably, secure and true to size.


Jeff: Ultraboost 21 upper uses adidas’ Primeknit+, their very fine knit that surprisingly doesn’t feel and breathe like a knit upper. 

It is constructed like a standard knit upper, integrating the tongue into the body, making it essentially resemble a big knit sock, albeit a soft, but not plush, big knit sock. 

adidas added soft pods inside the heel, to help grip the heel and prevent heel slip, with big plastic inserts on the outside of the heel counter. That gives the shoe lots of structure, in addition to the plastic midfoot cage adidas had done away with a few years ago. 

The plastic midfoot cage was lamented by many runners (it has also made its appearance on a number of various Boost equipped running shoes) for how it dug into the side of the foot while you ran. 

Luckily, this version seems very unobtrusive, and I didn’t notice it during any of my runs. However, it does mean that the shoe only has four eyelets, with no extra eyelet at the top (and the plastic construction means you can’t just use a leather punch to add your own eyelet) if you experience heel slip. And you might - I rarely have heel slip issues, but I had some here. The UB21 also utilizes their Primeblue technology, made of at least 50% reclaimed ocean plastic. It’s amazing that recycled plastic can feel as soft as it is - and aids ocean cleanup, which is always a nice thing. As one of RTR’s resident toebox snobs, I was initially impressed, but in time had issues. While the shape is good, there is a rubbery toe bumper giving the upper some shape up front, but that toe bumper created a rubbing sensation that threatened blisters on any run longer than an hour.

Sam: Most of the upper is made up of a toe box and midfoot side areas of very soft easily stretchy and breathable Primeknit+.

The rest of the upper (toe bumper, tongue, lower sides above the midsole collars is a soft suede like denser and thicker kint, Finally, we have the “3 Stripes” plastic cage which holds the laces and provides mid foot support. 

The rear collars and achilles hold up to the beginning of the integral knit tongue are densely and firmly padded. A  firm optic yellow plastic overlay wraps the far rear at the achilles but is lower there and with above the plastic soft dense padded knit. This means there is no hard plastic cup on the achilles. Rear lockdown is impeccably secure and comfortable.

Ivan: Ever since my first Energy Boost in the stretchy so-called ‘Tech Fit’ upper, I think Adidas had been in a class of its own when it comes to creating the perfect fit. This one is not only breathable, but also adapts well to the foot by the use of very stretchy and strong materials. 

I’m also happy to see that Adidas is focusing on sustainability with the so-called ‘Primeblue’ tech, as explained by my fellow RTR contributor. The shoe fits perfectly in my usual size US 8.5



I had no issues in the heel cup with the outwards flare ensuring that my sometimes sore  achilles tendons were not irritated. The midfoot was securely held in place with a reassuring midfood lockdown by the good old Adidas plastic cage. As already mentioned, the forefoot feels very plush and it didn’t cause me any issues despite being a bit tighter than previous versions, In terms of breathability, I didn’t end up with freezing toes despite the very low winter temperatures here in Scandinavia. 

In general the Primeknit+ seems nice and soft, but also a bit thick. I can not rule out that it may run a little hot in the summertime. However, I am not afraid of durability issues...apart from the fact that this good looking shoe will hardly stay white during these harsh winter months.


Jeff: adidas added roughly 6% more Boost capsules to the midsole from last year’s shoe, and anecdotally I’m surprised that number isn’t bigger. Between the little bit higher stack height and much wider platform, the overall volume feels like a big step up. The midsole is still made of nothing but Boost, along with a plastic plate system, which adidas calls LEP for “Linear Energy Push”. 

It is much more robust than previous plastic midsole inserts in the Ultraboost, their Torsion system, which was hard to see or feel. In this case, LEP is front and center. 

Not only for how big and yellow it is, but also for how exposed it is through the outsole - but I’ll go into that more in the ride section. The midsole has an interesting asymmetrical quality. I mean, every running shoe is asymmetrical, but in this case the medial side has a more exaggerated slope up, so that the overall midsole looks much higher than where the foot sits. 

Top: medial side      Bottom: lateral side

The measurable stack (total midsole and outsole, so not necessarily factoring where the foot sits) is ~26mm on the medial side, and ~21mm at the same point on the lateral side.

The underfoot platfom shape is much more exaggerated than previous models. 

I measured the forefoot, heel, and arch at the widest points to get a feel for how much change from the UB 20 there actually is. The forefoot of the UB21 was ~120mm (20 was ~116mm), teh UB 21 arch was ~83mm (20 was ~85mm), and the 21 heel was ~97mm (20 was ~93). While 4mm doesn’t sound like much, when it comes to platform width every millimeter makes a difference, including in weight.. The UB21 midsole also has a far more pronounced rocker geometry up front compared to last year’s shoe. It isn’t as extreme as the Saucony Endorphin Shift or ASICS Glideride, but a similar principle. 

Sam: The midsole is a massive sculpted stack of Boost with raised sidewalls into which the foot sits at the heel. 

As Jeff says, the medial Boost sidewalls are higher extending from an identical height on both sides just ahead of the heel further forward at that greater height than on the lateral side. I assume this is for some stability and support. There is plenty of that here!

The LEP system and rocker geometry, in combination with the extensive mostly firm outsole, clearly delivers a rigid rocker geometry here, said by adidas to be 15% stiffer than the UB20. It is not exactly a highly dynamic rocker effect due to the mass but an effective one to roll the foot forward smoothly at slower paces.  

There is plenty plenty of cushion here. I would call the overall midsole feel more highly protective and highly directed than plush, soft or bouncy due to the LEP and outsole in the mix. 

The LEP (Linear Energy Push) system here is well named. There is a clear sense after transitioning off the heel of a broad, stable, and mildly propulsive forefoot area, a giant platform to toe off from if you will. Of course, all of this is somewhat masked by the mass of the shoe but it is there and I would say effective. 

Adidas is obviously innovating in the propulsion plate area as the adios Pro with its Energy Rods is a spectacular racing innovation providing a clear sense the toes are in the mix and dynamically so for propulsion. 

Here the mission seems different: provide a stable front platform and rocker effect to move the shoe up and away at no matter how slow a pace. I hope adidas continues this concept in lighter trainers with say Lightstrike Pro foam, a far lighter and fun foam found in the adios Pro.

Ivan: I won’t get too much into details in regards to the overall geometry of the shoe as this has already been thoroughly explained. I think the very dominant heel section gives a visual impression that the thickness of the heel is more than the 30.5mm that is actually the case. Adidas has always been known for their Torsion system, which helps to achieve a more rigid and stable midsole that creates efficient linear propulsion. 

With my slight pronation and appreciating a more explosive toe-off I’m happy to report that I felt and enjoyed the new LEP system. With both more Boost, a relatively substantial upper and the new Torsion system, it is no surprise that the latest version is a heavy shoe. I felt this especially on my long runs, which I will return to in more detail later on. 


Jeff: The Ultraboost 21 outsole is a complete departure from the rubber Stretch Web outsole that has been on the bottom of every pair of Ultraboost before this iteration. This time around we have an exposed central channel of midsole and the plastic plate, surrounded by rubber rails lining the outside of the shoe, with a big rubber patch right in the middle of the forefoot. 

The quality of rubber seems very durable and grippy, with only the front branded Continental rubber. I do question the use of nearly half of the outsole being a clear crystal rubber, as after a few miles the shoe looks kind of dirty. Minor gripe, especially for a shoe with a number of other issues, but it’s a little awkward. The exposed midsole isn’t a problem though, it is recessed enough you aren’t going to get any kind of wear to the midsole. I experienced one fairly wet run in the Ultraboost 21, and didn’t experience any grip problems whatsoever.

Sam: adidas has gone very different than usual with the outsole here. Instead of “Stretch Web” covering the whole underside or extensive branded Continental rubber we have multi colored crystal type rubber at the heel and ringing the sides. It is thick, quite firm but with a bit of squish to pressing and is very tacky on the ground.

The center forefoot has a lozenge of what feels like a softer blown rubber I assume to soften toe offs and provide some give for the toes to engage. Up front we have a U shaped piece of Continental branded rubber for I assume wear resistance.

The outsole has that characteristic tacky feel of crystal rubber and should prove extremely durable. I agree with Jeff the white crystal rubber gets a bit dirty looking, and quickly, but once bought who admires outsole colors! And here this outsole is something to be admired when new in combination with the prominent optic yellow LEP piece which has so far stayed nice and shiny!

As Ivan has also noted the UB 20 is a very silent shoe for me as mostly a heel striker, a tribute to the give of the crystal rubber, the soft central forefoot and likely most especially in my experience due to the effective rocker geometry.

Ivan: Adidas' use of Continental - and now also partly crystal rubber - has always resulted in an unsurpassed grip on the roads. Even on the icy surfaces, I had no issues at all with grip. Also, it didn’t at any point feel clunky or sound noisy, which definitely can’t be said for all running shoes out there nowadays. Just a reassuring, stable and almost silent ride regardless of pace and surface. By the way, I really like the use of those bright outsole colors and the fact that you clearly notice the very yellow LEP piece. You won’t of course notice it yourself during the run, but then I guess you just gotta run in front to show it off...


Jeff: And this is where the shoe truly suffers. The ride was very awkward with every step, along with a pronounced “clop clop” sound with every foot fall. The sound is likely due to how close to the surface the LEP system is, and it’s a minor issue. The bigger issue is how odd the shoe runs. While more and more trainers are hitting new levels of smoothness in various ways, the Ultraboost 21 is the least smooth actual running shoe I’ve put miles in. For a shoe that is exceptionally heavy, the weight isn’t nearly the problem that the ride is for me. Another element, and it’s a big part of the problem for me, the midsole material. Boost has gotten even firmer in feel here, and it was already very firm. While there is a lot of cushioning underneath the foot, there isn’t much dynamic cushioning there - you don’t get any sort of sink in and rebound that you get with so many other midsoles on the market today. The heel slip issue I experienced was a tiny foot note compared to the awkward ride.

Sam: The ride is fine. Very stable and consistent with the rocker clearly felt and effective.  As a heel striker and given the shoe weight I decided this was for sure an easy and shorter days shoe for me. I tested as such but did pick up the pace a few times. I found that at pretty much any slower pace from 10:30 mile to 9:30 things went along very smoothly. No struggle off the heel on strike, very stable, densely and effectively cushioned with a very broad clearly felt forefoot and a mild but effective rocker up front off that broad forefoot with its LEP . A surprisingly effective ride for such a big shoe in all respects. Step on the gas and the weight is clearly felt, go further than say 7 miles and things get ponderous from the weight.

Ivan: I felt the very recognizable Boost ride all the way in the Ultraboost 21. A very pleasant heel-to-toe transition and efficient bounce, when just cruising along. The shoe is certainly not light, but the weight is very well distributed. 

I’m a fairly light runner myself with a high cadence , so during longer runs, I sometimes wished for a lighter and less of a “built-up” shoe. However, there is no doubt that most runners, especially heel strikers, will really benefit from the efficient transition though the entire gate cycle. However, don’t expect an extreme degree of shock absorption despite the appearance and the higher proportion of Boost foam. The new LEP torsion plate and a forefoot of just over 20mm does mean that it runs a bit firmer than one might expect. However, it is a fairly wide and stable shoe and overall a solid choice for most people who are going for short or medium distance runs with a reasonable amount of protection and efficient ride overall. 

Conclusions and Recommendations

Road Scoring Rubric

Jeff: I was truly excited to see what adidas had done, making big changes to a shoe that had big issues. Unfortunately, I found that they went the wrong way, making a heavy shoe that was under cushioned even heavier, not much more cushioned, and with a ride much worse than its predecessor for me, 

Aesthetics are top notch, but looking good isn’t nearly as important as running good, and these just don’t run very good. There are a number of shoes that cost less, weigh less, and run much better, with the Ultraboost 21 for me an awkward, at best, running shoe.

However, if you are looking for a top notch casual shoe it’s an expensive option, but a really good one.

I’ve been saying for a few years that adidas needs to move on from Boost as a midsole material, and looking at the rest of their lineup, it looks like that may be happening. Even if it means next year’s shoe is unfortunately called the “UltraLightStrike”, It would likely be a big step forward. 

Jeff’s Score: 6 / 10

Ride: 5 (50%) Fit: 8 (30%) Value: 6 (15%) Style: 10 (5%)

Sam: We mostly review performance running shoes at RoadTrailRun . Every runner’s performance and make up is personal-from the super fast to those just out for a few miles a day of jogging. If you are heading out for that shorter more mellow run, want a stable well cushioned ride, maybe are a bit heavier, are not a shoe gram counter, appreciate beautiful modern visual design and are not that concerned about price, the Ultraboost 21 it’s a fine choice.

I no longer run that fast or that long but the weight here was my most significant negative in terms of the ride, the UB21's versatility and ultimately the shoe’s value for me. And the weight comes in large part from all thatl Boost, a considerably heavier material than newer materials as well as from all that durable outsole, along with the dense and supportive knit upper from what I can tell. Drop 2 oz..  or more with more modern and energetic midsole foams such as maybe adidas own Lightstrike Pro as in the adios Pro, and a lighter upper and I expect the existing design of the Ultraboost would be a top contender for a max cushioned daily trainer for many more runners.  

The  Ultraboost 21’s primary purpose is clearly not “high performance” run training but to be an athletic styled and technically advanced and modern shoe that for sure can be run.. and do other things… and on its own terms, and look great doing it. 

I will continue to run it for no agenda, slower, easier and shorter runs where I want a stable, well cushioned ride. 

With the spectacular adios Pro as the brand’s flagship totally modern racer, the Ultraboost 21 sits at the other end of the spectrum as a triumph of shoe design with a lifestyle focus that can run some. Time to see what adidas comes up with between these two extremes

I score it for both as a performance run shoe and for what it is as described above.

Sam’s Score: 8.4 / 10

Ride: 8 (50%) Fit: 9 (30%) Value: 8 (15%) Style: 10 (5%)

Ivan: I think that Adidas has struck a fine balance in terms of design, quality, value and general performance. The already huge fan base for the Ultraboost will hardly be disappointed. 

Overall, the model will probably appeal especially to the many fashionable "everyday runners" and fitness categories, who mostly stick to a few shorter runs during the week. However, it’s also well suited for some experienced runners using it for especially easy days and recovery runs. Especially those wanting a fairly stable and wide platform. But this is definitely not a shoe for everyone. Especially considering that it’s possible to find softer and more cushioned alternatives in the same weight category nowadays. 

That being said, I think that a vast majority will be happy for such a good looking and well-balanced high quality running shoe which can be used for most runs, fitness and everyday life.

Ivan’s Scores: 9.0/10.0


Index to all RTR reviews: HERE

adidas Ultraboost 20 (RTR Review)

Jeff: The UB20 is lighter and a little less cushioned, but runs smoother. The extra width of the 21 platform is nice, but the LEP system ruins the geometry of the shoe for me. Both are top notch casual shoes.

Ivan: The predecessor was lighter, but I think the Ultraboost 21 is superior in most areas. Personally, I like the design better and quality seems even higher. The ride itself, especially with the new LEP torsion system, also feels more efficient and balanced.

ASICS Glideride 2 (RTR Review)

Sam: Both shoes have a rigid rocker profile. The Glideride 2  approach is yet more prescriptive and pronounced than the UB21. It has a very distinct rocker effect that kicks in when running with the ankle essentially immobilized to drive the foot forward very consistently in the line of travel. This said walking around in them is not much fun, unlike UB 21  Glideride is at least as cushioned and somewhat softer with a similar stable firmer forefoot from its embedded EVA plate. The Glideride is a superior (dedicated) run trainer .


ASICS Gel Nimbus 23 (RTR Review)

Jeff: The Nimbus 23 isn’t the most plush ride out there, but in a L/R comparison it has substantially more squish and rebound than the mostly static Ultraboost. The upper is much more plush, with more room in the toe box, and the midsole, while thinner is also more effective, with more flexibility leading to a much smoother run.

Brooks Glycerin 19 (RTR Review)

Jeff: Brooks hit a home run this year, similarly making a wider platform up front, but they also made their DNA Loft midsole more plush and bouncy. If the prices were swapped and the Brooks was $30 more, it’d be worth it, at $30 less it’s the easiest call you’ll make.

Mizuno Wave Sky Neo (RTR Review)

Jeff: Similarly heavy and costly, the Wave Sky Neo has yet to come to the US (but those who have used Google before can likely find a retailer that will send them to the US) but it’s midsole is the polar opposite in cushioning. Uppers are very similar, and overall I think I prefer the shape of the UB21 midsole, but the way the cushioning is used is superior in the Mizuno. 

New Balance 1080v11 (RTR Review)

Jeff: The most recent 1080 was a slight step back for me, with few changes from the really good v10 (except for a short heel cap that caused various levels of pain and discomfort every moment the shoe was on my foot), but it’s still a big step up from the Ultraboost. Cheaper, lighter, more effective cushioning, the only place the adidas wins is in the looks department.

Ivan: The new 1080V11 is a lighter shoe, better suited for those faster and perhaps also longer runs. However, to me it doesn’t have the same energy return and deeper cushion. It has more of a dampening sensation to its cushion. Also, the upper is not as form fitting, something  I really enjoy in the UB 20.

Sam: I concur 100% with Ivan on the almost 4 oz lighter 1080v11

Nike React Infinity Run FK 1 (RTR Review)

Jeff: The Infinity had some issues for me, major heel slip (remedied with some surgery with a leather punch to add eyelets) and constant arch irritation from the support system were the main ones, but those problems pale in comparison to the UB21 and how awkwardly it runs.

Ivan: The Infinity model is even wider and more stable than the UB21. However, I clearly prefer Boost over the more dense feeling React foam, which also suffers from being temperature sensitive in the cold. Also, I had some serious issues regarding the fit of the Infinity, especially around the heel area.

Sam: The UB 21 wins on all counts over React Infinity except… weight. The Infinity React’s Flyknit upper was awkward fitting and its side rails spoiled an otherwise very decent ride whereas the LEP and outsole of the UB21 provided not only stability but a smoother transition and rocker. 

Nike ZoomX Invincible Run FK (RTR Review)

Jeff: This just seems unfair. Two shoes at the same price point, released around the same time, both aiming to be big cushion for big miles. One absolutely outkicked the coverage, putting out one of the bounciest shoes ever made, and the other one of the least responsive shoes. Both knit uppers were steps forward, but the Ultraboost 21 midsole doesn’t work, and the Invincible midsole belongs in a museum.

Sam: Totally agree with Jeff here!  Far lighter, far more dynamic and faster the Invincible as the max cushion dedicated run trainer from Nike beats the UB21 when it comes to running versatility and fun. The picture changes if you're looking for a more stable, likely more durable, more lifestyle oriented shoe that can do some running and with clearly superior visuals and a far more refined upper. For those purposes the UB21 is clearly worthy of consideration. 

Saucony Endorphin Shift (RTR Review)

Jeff: Similarly firm, the Endorphin Shift clearly leans into by using geometry that makes the shoe roll from step to step, instead of the bounce that so many big stack trainers rely on. It might not be the shoe for everybody, but it’s a very interesting and fun ride - and in a head to head showdown with the UB21, there’s no hesitation to go Endorphin.

Sam: As with the Invincible if for pure run training  for sure the lighter Shift and I say pure run training as the rocker geometry of the Shift really works best when running whereas the UB21 rocker feels just as good walking as running . The UB21 winning on aesthetics over the chunky in comparison Shift but at a price of $40 more.

Saucony Triumph 18 (RTR Review)

Jeff: Nicely cushioned with a very plush ride, Saucony’s PWRRUN+ midsole is frequently compared to Boost both are expanded TPU pellets based, but when worn at the same time it’s staggering just how much more give and rebound the Saucony midsole has. Save the money, get the Saucony.

Sam: A closer match up than some of the others here for me. The Triumph weighs an ounce less. It has a much flatter traditional geometry and no propulsion element as the adidas does. As both for me would be dedicated to slower easy shorter runs I prefer the “help” the LEP and rocker provide in the UB 21 as well as its aesthetics and can put up with its considerable weight.  

Mizuno Waverider 24  (RTR Review)

Ivan: This classic from Mizuno hardly wins any design awards, but it’s an excellent everyday and long distance trainer. It is also quite stable with the wave plate technology and the lower weight makes it more versatile. However, it feels much firmer on the run, which may not appeal to everyone.

Asics Novablast  (RTR Review)

Ivan: The Novablast is lighter and bouncier. It is suitable for all kinds of rides, but the overall quality and fit is not at all on par with the Ultraboost 21. At the same time, it is also somewhat unstable, which may exclude some runners from buying it.

Sam: Novablast delivers lots of bouncy fun and is far lightert. It is also far less stable and substantial but none the less highly cushioned and an exciting ride. Neither would be a good daily trainer choice for for me  but I might pair Novablast as the short fun faster run shoe with the UB 21 as the slow short and easy days shoe but would have a more suitable daily trainer and an uptempo longer run shoe in my rotation. 




Tester Profiles

Jeff is the token slow runner of the RTR lineup as such his viewpoints on shoe and gear can differ from those who routinely finish marathons in three hours or less. Jeff runs 40 miles per week, both roads and desert trails in Phoenix, Arizona. He has a PR's of 4:07 marathon and 5K at 23:39. In December 2019 he raced his first 50 mile trail ultra. 

Ivan Luca Corda: Copenhagen, Denmark.

Current age group: 45+. Height: 5’11 Weight: 140 lbs

Began running in 2012 (age 36). Weekly mileage: 50-80 miles (mostly roads and light paths/trails) Favorite distance: Marathon. Memorable running experiences: Tromsø Midnight Sun Marathon ‘17 (above Arctic Circle starting at midnight in full daylight), Valencia Marathon PB in 2019 in 2:39:28, First Ultramarathon in 2020 (100 km) and 3rd at Danish National Championship

Passionate about analyzing all sort of data by using every possible gadget. This also includes comparing running shoes by measuring running mechanics.

Sam is the Editor and Founder of Road Trail Run. He is 63 with a 2018 3:40 Boston qualifier. Sam has been running for over 48 years and has a 2:28 marathon PR. These days he runs halves in the just sub 1:40 range training 30-40 miles per week mostly at moderate paces on the roads and trails of New Hampshire and Utah. He is 5’9” tall and weighs about 164 lbs.

Tested samples were provided at no charge for review purposes. No other compensation was received fly RTR or the author for this review from adidas . The opinions herein are entirely the authors'.

Comments and Questions Welcome Below!
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Anonymous said...

Just a reflection - one of my original running shoes was the ultraboost. Compared to many running shoes now its is so heavy and can feel like you running in sand as its so soft. I think boost has had its day, the newer foam are far superior in weight and energy return- peba, zoom x, fuelcell etc. I still enjoy the ultarboost for its comfort though - like walking on clouds but can no longer runs in them. :)

Anonymous said...

Adidas Solarglide 19 is one of my all time favourite shoes for daily mileage (I´ve been runnng since 1979), so there are recent examples of successful Boost shoes (you can even use it for tempos if you need extra protection and stability). I also bought UB20, but that was unrunnable and I use it as a casual shoe, so I don´t think I will bother with the UB21.