Merrell MTL Skyfire 2 Review: These Crazy-Light Trail Runners Are Ready to Fly

I’ve been wearing a pair of the new Merrell MTL Skyfire 2 trail runners for the past few months, and these shoes are fast. When I first slid my feet into them, I immediately wanted to run up the nearest mountain.

While no shoe can actually propel you up a hill, the Skyfire 2 comes close. Every climb in these shoes feels like the fastest I’ve done that hill, and it usually is. They’re crazy fun when you point them down the mountain as well.

In short: The 2023 Skyfire 2s are quick, agile, and grippy. These are some of the lightest trail running shoes you’ll find. With deep lugs, a Vibram Megagrip outsole, and a rigid midsole, they’re at home going fast on technical trails with plenty of elevation gain and loss.

Merrell MTL Skyfire 2 Review

Crazy-Light Shoes

The Skyfire 2 is light enough to make hills feel almost effortless. At under 14 ounces for a pair of men’s size 9, these are insanely light for a trail runner. My men’s size 9.5 weighed 6.88 on one scale, and 7.2 ounces per shoe on my home scale — putting them around 7 ounces for a size 9.

They feel almost like track cleats in many ways: the protection underfoot is minimal, the last is narrow by trail shoe standards, and the mesh upper wraps under the arch in that snug way that track shoe fits.

There isn’t much to these shoes, but there’s just enough to make them trail-worthy. They have a lightweight engineered mesh upper and enough stack for rougher terrain. They’re comfortable enough for all-day runs, but that’s mostly because they don’t weigh you down. 

The Vibram Megagrip outsole is a custom-molded web of rubber and 5mm lugs. The outsole doesn’t completely cover the midsole foam, and the most significant weight savings come from this minimal approach to an outsole (more on this below). 

These aren’t your workhorse shoes for every run. But when you do put lace them up, you’ll immediately feel the difference between these and the other trail runners in your quiver. Mostly, you’ll feel the way you don’t feel these shoes on your feet. 

Impressive Traction

The Skyfire 2 uses a minimal amount of Vibram rubber in the outsole and large sections of exposed midsole foam to save weight. Merrell makes every ounce of rubber count here. The rubber is everywhere you need it, and thankfully, the Megagrip compound grips extremely well in wet and dry conditions.

The 5mm multidirectional lugs bite into dirt and mud as you push off in any direction and when braking. The highly stable upper also feels locked into the midsole, which adds to the impressive traction.

FlexPlate and FloatPro Midsole 

The Skyfire 2 uses a lightweight FlexPlate in the midsole, which adds rigidity and increases efficiency as you push off. It also adds to the shoe’s overall stability by supporting your foot laterally. 

Instead of sitting above or below the midsole like a rock guard, the FlexPlate is sandwiched between the FloatPro midsole foam. On its own, the FloatPro midsole is light and snappy. It gives enough cushion but is also responsive enough not to feel spongy as you push off the ground. 

With the FlexPlate built into the midsole, it’s even more efficient. All that energy you put into pushing off your forefoot gets translated into propelling you down the trail. There’s no unneeded flex to lose power, but it’s not so stiff that it’s uncomfortable, either. 

The FlexPlate also creates a very stable platform as you drive with the front of your foot. These shoes have little side-to-side flex, which keeps your foot securely in place as you push off laterally. 

Conclusion: Fantastic but Not for Every Run

The Skyfire 2 is designed for race days, FKT attempts, and other trail runs where performance and speed are crucial. 

As much as I’d love to wear these for every run, they wouldn’t last long enough to make everyday use practical. This is possibly the shoe’s only big downside. They’re comfortable enough to wear daily, and it’s a joy to feel your fastest while wearing these shoes, but they’re not built for that. 

After logging about 100 miles on these shoes, the midsole looks like it’s seen a fair amount of sharp edges of rocks. The exposed foam on the midsole simply won’t stand up to several hundred miles on rugged terrain like a heavier shoe would. 

This isn’t a surprise, and I’m not complaining, either. All the exposed foam means is the outsole is as light as possible for the days when you do lace up in the Skyfire 2s. They’re more than durable enough to handle 200-300 miles, but I wouldn’t expect these shoes to last you more than that if used often on the rugged, rocky terrain they’re capable of.