Saturday, August 05, 2023

Nike InfinityRN 4 Initial Review: Soft, Bouncy and Pleasing! From Nike?

Article by Sam Winebaum

Nike InfinityRN 4 ($160)

Update: Our full multi tester review with 8 comparisons is posted HERE

The softest bounciest most mellow riding Nike I can recall 

The Infinity gets a new React X foam midsole and unlike prior React it is considerably softer on the run and with 13% more energy return according to Nike. Processed using direct injection instead of compression molding, the midsole's carbon footprint is reduced 43%. 

I would say it is one of the softest foams out there and quite a shift in direction from Nike’s older React. It is not as silking springy as ZoomX, more closely resembling New Balance Fresh Foam in shoes such as the More but due to geometry, outsole and 9m drop with a less mushy and ponderous ride. 

I was surprised how soft and bouncy the midsole was during my first 4 mile run on very tired legs from a rugged rocky hike the day before. Just what my tired legs needed! Yet I was also surprised that my pace at 10:19 per mile was decent and easy and I had plenty of stability to go with the softness and rebound. Please read on for all the details.

Big Stack Height and Stable Geometry

We have a giant 39mm heel / 30 mm forefoot full stack height. The stack height is the same as the Invincible Run 3 and is 5mm more at the heel and 4 mm more at the forefoot than the Infinity Run 3. Compared to the Infinity 3 we do gain 0.7 oz / 20g which can be explained by this increased stack height.


The big stack height and React X foam translates to a super cushioned ride with the extensive well segmented outsole providing some mild response, at the ground stability and decent flexibility. It also means the RN4 is not a light shoe as my US9 sample checks in at 11.16 oz / 316g. I will say it runs lighter than its weight due to its energetic if soft midsole and 9mm drop geometry.

The RN4 clearly has inherent stability features but I would call them of the most mild variety compared to any I have run recently (Brooks Glycerin GTS, and even Kayano 30 and Puma ForeverRun among others).

The stability starts with the broad platform, 90mm wide at the heel, a moderate 70mm at the midfoot (to help with transitions) and a giant 120mm upfront (the widest I can recall and I think essential to keeping the soft foam up front stable enough)

The mild support guidance continues with high rear midsole side walls of the same foam as the midsole, so soft and in no way the quite harsh glued in extended plastic clips of prior Infinity. The Infinity shoe I just struggled to transition off the heel in due to the clips' rigid nature and on both sides of the shoe. The walls rise to the same height on both sides of the shoe with the foot sitting down as much as about 15mm in the walls to the top of the insole. Not worry the walls are soft and adaptive.

On the lateral side (top below) we have a concave shaping of the side walls to create a lateral crash pad and aid decoupling. Clearly felt and effective!

On the medial side (bottom above) the shaping is convex for some stability. Also clearly felt as a touch of additional support but as the foam is soft the support is adaptive to my more neutral strike and in no way felt as any additional medial firmness or a sharper edge (as with plastic clips) at the top of the midsole such as in the Infinity 1-3..

Comfort Stretch Flyknit Upper 

The first two words "Comfort Stretch" are key. This Flyknit is very stretchy and foot shape adaptive, maybe to a fault for low volume feet but likely will be a joy for wider higher volume ones. Again, as with the midsole, Nike is going a new direction with a far more easy going and comfort focused upper and a sharp contrast to the Invincible Run 3’s upper or any prior Nike I can recall.

The mesh is stretchy with raised tufts whose thickness I am guessing helping with support. 

The toe box for sure is stretchy and broad and has no toe bumper stiffening beyond the raised outsole up front. I had good hold but the stretch started to be noticeable at faster paces with some lockdown there starting to go. A bit of toe bumper stiffening may be in order.

Wisely, Nike includes a gusset tongue and midfoot hold is excellent but I do notice a bit of lace bite as I have to cinch the laces quite tight for my lower volume feet to take up the stretch. I doubt higher volume feet will have this issue.

The heel counter is not particularly rigid with rigid heel counters often seen in “support” shoes The red rear strap provides most of its structure along along with the raised midsole side walls further forward.

Nike sent me a half size up from my normal US8.5 and I think it is mostly the right call although I wonder if the slight sense of not enough toe box hold at faster paces would be reduced at true to size. At half size up I will say length is correct at about a thumb's width but with such a soft upper and no real toe bumper getting closer to the front might not be an issue.

I do think I could go true to size with my narrower lower volume foot but those with higher volume feet should try the half size up. 

 Ride and Recommendations

Lots of very friendly “React-ive” cushioning here of the very soft and bouncy variety, The combination of mellow rear stability elements and 9mm drop had me easily transitioning forward at any pace, even slow ones. Often soft high stack shoes (Endorphin Shift 3, Fresh Foam More) can be ponderous at slow paces but not at all here. At faster paces, due to the upper, things were not quite as locked down and things got a bit more bouncy but I focused on hitting the 30mm forefoot squarely and I moved along with big smiles.  At 11.16 oz weight is up there and I wish we were closer to 10 oz but the lively ride had me mostly forget the weight. Same shoe with Zoom X I say!

There is not as much of the wild Zoom X fun and relative instability of the Invincible Run 1/2 and none of the over prescriptive “guidance” from its plastic rails of the Infinity 1-3 here. And if you are a Pegasus fan with its traditional React and Air, the RN 4 is far more cushioned and not as firm and also not as responsive snappy and quick off the road. Save the Pegs for tempo work and light trails. Compared to the Invincible Run 3, we have more flex and a more sophisticated geometry, easier slower paces manners but not quite as dynamic faster paced ones due to the softness, and while not quite as locked down way up front a better more comfortable heel hold and more comfort focused upper overall. 

For the faster higher mileage runner so far I am seeing the RN4 as a wonderful easy days, recovery miles, and for some long run shoe given its soft mellow but in no way ponderous ride with plenty of upper room and a touch of mellow guidance to help direct the softness. 

For the more recreational runner or beginner, walkers, and those on their feet long hours who seek a soft, highly cushioned, easy to turn over and pleasing experience-top to bottom, the InfinityRN 4 is a great new option and certainly is for all Nike fans who felt React was too firm and not particularly “reactive”. 

Update: Our full multi tester review with 8 comparisons is posted HERE

The Nike InfinityRN 4 is available now including at our partners below 

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Samples were provided at no charge for review purposes. RoadTrail Run has affiliate partnerships and may earn commission on products purchased via shopping links in this article. These partnerships do not influence our editorial content. The opinions herein are entirely the authors'.

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