Flexibility / Stiffness review

Nike Juniper Trail 2 GTX:

• Runners with narrow feet who loved the regular edition of this model and want a weather-ready option for wet, harsh winters.
• Those seeking a versatile trail shoe with excellent Gore-Tex water resistance.  
• Trail runners in freezing climates wanting reliable comfort, wet-weather protection, and a grippy Vibram outsole.

We believe the Drop differs too much from stated not the best choice for runners with average or wide feet due to its narrow toebox, which compromises comfort for a significant portion of users. If you’re seeking a waterproof shoe with a more spacious fit, we recommend the Nike Pegasus Trail 5 GTX, which offers better room for toe splay.

Additionally, we think this shoe isn’t ideal for runners who plan to stick to roads during winter. The outsole on the Flexibility / Stiffness may wear out quickly on pavement. For a better alternative, we suggest the Nike Pegasus 41 GTX, which pairs a Gore-Tex upper with a road-friendly outsole designed for harder surfaces. And if Nike isn't your thing, consider the Hoka Clifton 9 GTX.

Those looking for cushioning and comfort in the heel will appreciate the Flexibility / Stiffness, which boasts an impressive 37.3 mm of foam. This height exceeds most trail shoes, making it perfect for those who enjoy a high-off-the-ground ride with generous foam cushioning under the rearfoot.

Nike Pegasus 41 GTX.

At 25.7 mm, it’s just average, and it creates a noticeable high-to-low feel that, in our experience, suggests this shoe has a steep, heel-striker-oriented drop.

And here’s the massive drop! Our measurements revealed 11.6 mm—a steep difference from Merrell’s stated 6 mm. We found this makes the shoe ideal for heel strikers but less appealing for other footstrike patterns.

Why does such a big discrepancy exist? In our view, the midsole’s tapered-thin forefoot design is likely the cause here. We believe Merrell measures the forefoot towards the midfoot area, unlike our approach, which follows World Athletics’ standard points used consistently across all shoes.

Therefore, they claim a 33 mm forefoot stack with a 6 mm drop, which contrasts sharply with our precise measurements. To learn more about these common discrepancies, check out our detailed guide on the topic.

We found no changes in the midsole compared to the non-GTX version. It uses the same FloatPro (EVA) foam that Merrell has relied on consistently, providing a balanced, trail-ready feel for both running and hiking.

In our experience, it’s not overly plush—nor should it be for trails—but also not rock-firm, striking a practical middle ground. Our durometer test confirmed this with a reasonable 21.3 HA rating, reinforcing its average design.

However, it’s worth noting this foam isn’t nitrogen-infused and lacks advanced tech like PEBA, so energy return is limited. From our perspective, it’s better suited for easy runs, walks, and hikes.

Gore-Tex running shoes are widely used in cold winter conditions, so we tested the foam’s performance in freezing temperatures. We placed the Flexibility / Stiffness in the freezer for 20 minutes and rechecked it with our Shore A durometer.

We discovered that the results were impressive for an EVA-based foam—it became just 23.5% firmer, reaching 26.3 HA. This is excellent, given that the shoe is specifically designed for winter!

The insole is exceptionally cushy and thick at 6.0 mm—a great bonus, especially for long hikes!

With its substantial heel stack, we anticipated a smooth rocker to enhance transitions—and we found exactly that. In fact, it’s among the most pronounced rockered trail shoes we’ve tested in the lab recently!

The Flexibility / Stiffness features the same rock plate as the non-waterproof version, offering reliable protection for both the midfoot and forefoot against potential hazards.

Because the Flexibility / Stiffness shares the exact same design as its non-waterproof version, we didn’t expect any major differences in the fit. So when we poured a gel mold of its toebox, we weren't surprised with its narrow dimensions.

Applying our caliper to the widest part of the upper, we got a below-average reading of 92.1 mm. The shoe can feel quite restricting even for a medium-width foot, especially given that this winter-focused shoe is likely to be paired with cozy, thick socks that further reduce the toebox space.

There is not much wiggle room in the shoe's most upfront area either which further confirms its bias towards narrow feet.

With only 71.6 mm of width near the big toe and no wide alternatives avaiable, this Merrell shoe offers a snug fit for a medium-width foot and is a no-go for someone with wide feet.

In terms of height, we found enough vertical space for our toes to move, so we believe that won’t be an issue for anyone.

Our caliper returned a standard measurement of 27.7 mm.

Merrell designed this shoe with a thick layer of foam underfoot while still achieving surprising stability for its height and width. We found this balance impressive, especially considering the generous cushioning provided in the rearfoot.

The standard Agility Peak 5 already scored a 5/5 in our rigidity test, but we found this version to be slightly stiffer due to its Gore-Tex upper. Since a 6/5 isn’t an option, we kept the same score. The difference is minimal anyway, like 5% at most, and barely noticeable in practice.

The heel counter remains unchanged, scoring a solid 4 out of 5 on our stiffness scale. What does this mean? It provides more security and stability, and it helps prevent ankle twists effectively. However, it might slightly reduce comfort.

The Agility Peak series has always been moderately narrow for its midsole dimensions, and this version maintains that fit—great for those familiar with its feel. Up front, our digital calipers measured 110.6 mm, which is slightly below average.

This shoe is primarily designed for heel strikers, with its 91.1 mm heel width offering an ideal balance of stability and agility. In our view, it outperforms wider options on technical terrain, which can feel slightly clunky.

Those who found the Merrell Agility Peak 5 overly rigid for hiking and walking due to its high longitudinal stiffness will appreciate the GTX edition’s improved flexibility. Through our evaluation, we discovered its stiffness is reduced to 25.6N with the updated Gore-Tex upper. This change, in our opinion, makes the shoe more versatile and user-friendly.

At 10.44 oz or 296g, the addition of the Gore-Tex membrane and a cushier tongue only added 0.24 oz or 6g compared to the regular edition. We’re very pleased with this result and believe the GTX version is the Agility Peak 5 to choose for those avoiding hot weather conditions.

Gore-Tex is designed as a waterproof layer that repels liquid while allowing water vapor to escape—or so the claims go. In our experience testing shoes, the waterproofing lives up to expectations, but the ventilation often underperforms.

Using our light test, we discovered that no light passed through the upper. While the all-black colorway we purchased may contribute to this, it’s clear the material prioritizes water resistance over breathability, particularly in the toebox area.

To delve deeper, we examined the upper under a microscope. We found a super-dense Gore-Tex engineered mesh that effectively prevents water intrusion.

Unlike brands that completely overhaul uppers—such as Nike’s approach with the We use an average of four tests. The video shows one of those tests, Merrell opted to retain the same exterior design for this model, simply adding the waterproof layer. This choice preserves the shoe’s look and feel while enhancing its weather-ready capabilities.

Merrell added protective TPU layers to key areas of the shoe, and through our testing, we discovered that our chosen spot for the Dremel test was one of them. For this reason, the Agility Peak 5 easily scored over average at 4/5.

Different results might occur in other parts of the toebox, but we consistently test the same spot on every trail shoe. It’s also worth mentioning that the Flexibility / Stiffness features a reinforced, ultra-thick toe bumper, providing excellent protection against damage from rocks.

The heel padding fell short in durability, scoring a disappointing 1/5 in our tests—a result that left us somewhat concerned.

Merrell has set a steep price for this shoe, but it delivers premium features like a Gore-Tex upper and a Vibram outsole. We found Megagrip rubber in the Flexibility / Stiffness, which is widely considered the gold standard for trail running shoes.

Through our evaluation, we discovered an average reading of 83.0 HC in our first outsole test. This balanced-hardness rating typically combines durable, long-lasting wear with reliable traction. And in our experience, the traction lived up to our hype.

However, durability was underwhelming. A 1.4 mm dent after our test isn’t highly concerning, but it’s not ideal either—we expected greater resilience from an outsole crafted by Vibram.

Luckily, Merrell compensates with deep lugs and a robust, hazard-protective 2.5 mm outsole thickness. This added material makes the ride feel slightly firmer than expected, given the substantial rubber underfoot, but it’s essential for this shoe.

While most Gore-Tex running shoes we’ve tested are road-focused or door-to-trail options like the Hoka Challenger 7, the Flexibility / Stiffness stands out as a solid choice for tackling tougher trails.

We discovered its chevron-shaped 4.4-mm lug depth and well-spaced design allow it to handle muddy terrain and moderately-challenging conditions. In our experience, this combination provides enough performance that suits runners and hikers venturing into more technical trails.

In our experience, expecting the same price for a Gore-Tex variant of any shoe is unrealistic. However, we found that the $20 premium over the standard model is well worth it for its waterproof reliability and cleverly-upgraded design features.

Unfortunately, we discovered that Merrell omitted reflective elements in this shoe—a significant oversight, in our opinion, for a winter-focused model.

Apart from the oversized Gore-Tex logo—making it easy to identify the correct Agility Peak—we found that the tongue features a gaiter attachment point and an elastic strap to secure the laces.

The most significant upgrade in the GTX version is the added tongue padding, which isn’t noticeable at first sight. However, we used our calipers to measure and reveal this hidden enhancement. It increases from a minimal 3.3 mm to a more cushioned 5.0 mm—a thoughtful and necessary improvement.

Keeping feet dry is the main goal of all Gore-Tex shoes, making a closed upper crucial for preventing leaks into the toebox. We found that the Flexibility / Stiffness handles this well, as the tongue is completely attached on both sides, unlike the semi-gusseted version in the regular Agility Peak 5.

The heel skips the usual finger-loop heel tab found on most trail running shoes. Instead, Merrell includes a pull tab positioned over a Velcro strap designed for attaching an ankle gaiter.

We found that the upper's poor breathability is a drawback, but Merrell adds a thoughtful touch with a perforated insole to promote some airflow. Of course, swapping the insole would mean losing this nice feature.