Review: Montrail FluidFlex ST-Stable, Supportive, Low Slung Trail Runner

The Montrail FluidFlex ST is a 9.4 oz/ 266 gram 22mm heel/18mm forefoot trail runner with a stable supportive ride. $95, so a very good value compared to many 2015 trail runners. Lightweight and agile, the overall package has a substantial seamless upper, great rock protection and an innovative variable density midsole, the Fluid Frame. While the shoe is called out for "over pronators" this resolutely neutral runner, who can't stand stability and support features in most shoes, found the firmer mid foot midsole foam just right for rougher trail stability and confidence. I sized up half a size and fit is perfect.

Montrail FluidFlex ST

I have run up to 16 miles on easier smooth Utah trails, some roads, and rough, rooty, rocky NH trails. The FluidFlex ST handled all terrain with ease and comfort but one would say, if used as road trail hybrid, it would lean towards trail. While I have not run in the Fluid Flex the key difference between the 2 shoes is the FluidFrame midsole and its increased stability

Fluid Frame
The special sauce in the FluidFlex ST is the midsole.
Essentially Montrail  uses a patented process to layer in raw materials that when heated and compressed will produce different densities and thus firmnesses in a smoother gradient than the typical glued in posts and firmer mid foot stability foams. The result is superb torsional rigidity, great stability on rough terrain, a decently cushioned heel, and flexible protected forefoot if a bit awkwardly flexible so due to the forefoot rock plate.

Montrail Fluid Frame

"Small pellets of varied density foam are hand poured into a mold in a layering process that creates the density/durometer gradient. That mold is heated and expands into one large contiguous pieces of foam. Which ultimately is put into the final compression mold to become the midsole."

The midsole is thus all of the same material blending and quite seamless feeling in terms of ride. No posts, no adhesives, not sensation of dramatic differences between segments of the midsole. Others may take this approach or something similar but I haven't seen it.

So the result is a relatively soft heel (gray foam), firm supportive mid foot (white and gray foam) then softer under the forefoot protected by the rock plate (gray foam). 

Montrail FluidFlex ST 

Outsole

The outsole is Montrail's Gryptonite sticky rubber arrayed in a Micro 3 Point Lug configuration. I find this arrangement a decent compromise for most terrain. The exposed midsole under the midsole is relatively firm and thus should be quite durable, but it is exposed. To achieve the sub 10 oz weight with supportive upper and stable midsole something had to go, outsole coverage, where it is not really needed.

A deep flex groove under the ball of the foot makes the FluidFlex ST a decent climber despite the firm and stiff composite rock plate. The flex is a little strange and discontinuous as it goes from great flexibility at the ball of the foot to stiff under the plate and then more flexible up front by the toes. Not really noticeable on any terrain except maybe moderate uphills at speed where it feels a touch awkward.

Upper

The upper is excellent. Very supportive, snug around the heel and mid foot with a narrower but in no way binding front of the shoe. 5 seamless overlays are tied into the laces. Where the dark red inverted  Y overlays meet the midsole thicker overlays fill the gap in the same pattern on either side of the shoe.

Montrail FluidFlex ST

When the stable platform is combined with the upper I have felt well supported and confident, not always the case in a sub 10 oz trail shoe.  Softer mesh over the toes is combined with denser more supportive mesh in the mid foot.

Montrail FluidFlex ST

The toe bumper is decently firm combing a sewn overlay with a coating of ground rubber but, unlike many trail shoes. the toe bumper is not noticeable on the run. Debris sneaking in has not been an issue. The tongue is decently padded but not overdone  The heel collar is firm and well padded. Quite an improvement in upper stability when compared to the Montrail Bajada of a few years ago where the upper collapsed medially after relatively few miles. The Bajada II shares many of its  upper characteristics with the Fluid Flex ST including a similar more robust upper. More miles will tell me if the upper remains solid but I believe it will.

Ride and Recommendations

While billed as a trail runner with some pronation control, and I can't stand pronation control shoes, I have found the FluidFlex ST to be a stable, light, agile trail runner for just about any terrain and especially rougher terrain where the low slung platform really shines. It is also quite fine on the road, if a bit firm, making it a good door to trail shoe. It is very decently priced at $95. Never a fan of super light, super flexible trail runners, preferring more cushioning and stability the FluidFlex St may not be the shoe I run for really long runs on moderate terrain (Hoka Challenger ATR or Speedgoat, adidas Raven Boost)  or fast runs on smooth terrain (adidas Adizero XT Boost) but for those in between distances on rougher terrain it is a fine blend of protection, agility, and stability all at less than 10oz weight.

The FluidFlex ST were provided to me at no charge by Montrail. The opinions herein are entirely my own.

The Montrail FluidFlex ST is available at Running Warehouse US, now:  Men's here Women's here.  FluidFlex ST is on sale for $66.50 (ends 6/14) . All purchases at these links support my blog. Thanks!