Merrell MTL Skyfire 2 Review

An in-depth review of the Merrell MTL Skyfire 2 trail running shoe.

By on August 15, 2023 | Comments

You’d be forgiven if you blinked over the last decade and didn’t notice what the shoe designers at Merrell — particularly in trail running — have been up to. What many of us know as a common hiking-shoe manufacturer has snuck up on trail runners in a major way with the new Merrell MTL Skyfire 2 ($200).

The “MTL” in the shoe’s name stands for “Merrell Test Lab” and the brand is carving out a space for this high-performance division with its own social media feeds that are separate from the general Merrell account and where the messaging is all about design uniqueness, experimental concepts, and a stated mission to “make the MTL Skyfire 2 the running shoe with the most FKTs [fastest known times] on earth.”

This is a “super shoe” but not like the ones taking down records on the road; it’s a confounding mix of super lightweight with strong materials that can inspire speed going up and down as quickly as possible. I’ve become something of an expert in lightweight, short distance trail running shoes, so I’ve got many pairs of shoes to reference when the application is fast running for short distances, particularly up and down steep mountains.

I’ll get into the reasons that the MTL Skyfire 2 is not flawless, but in terms of a shoe that will help you PR or FKT this is one to strongly consider.

In terms of stats, this shoe weighs 7.1 ounces (200 grams) in a U.S. men’s 9, and has 6 millimeters of drop.

Make sure to also have a look at our Best Lightweight Trail Running Shoes article, where we’ve named the Merrell MTL Skyfire 2 the best lightweight shoe for technical terrain.

Shop the Men's Merrell MTL Skyfire 2Shop the Women's Merrell MTL Skyfire 2

Merrell MTL Skyfire 2

The Merrell MTL Skyfire 2. All photos: iRunFar/Bryon Powell

Merrell MTL Skyfire 2 Upper

Though I didn’t test the original version, the Merrell MTL Skyfire 2 cuts a drastic departure from the first MTL Skyfire. The original shares much more of its common characteristics with what you’d expect in Merrell’s days of old. And although the MTL Skyfire 2 also uses a TPU upper with breathable engineered mesh, the look is much different.

Firstly, the Merrell Test Lab sought to give the MTL Skyfire 2 nothing extra, so it’s not surprising that the upper is very stripped down and you can even see through it.

The tongue is not gusseted and it’s paper thin, but I’ve had no trouble with it slipping or becoming irritable. A punch out at the top right of the tongue increases air flow and removes some material, seemingly as a weight saver.

A millimeter-wide elastic band is sewn to either side of the upper over the shoelaces; this nifty detail serves as a barely there lace garage.

Below the tall heel collar, there are sewn-in inserts of padding but it’s a little lower on the heel than most manufacturers opt for. I really like the sensation and support, and it also adds some debris protection.

For me the shoe runs true to size, but one might want to size down a tad as the heel could be a little sloppy if too big. The hard plastic FlexPlate heel counter is very effective at keeping the arch in place and locked down.

A small, welded overlay on the inside and outside of the upper serves to stop rips or tears. Speaking of which, though it has mostly stood up to the elements, the upper has suffered a small tear near my big toe. I don’t feel this upper material is as strong as the now common Maytrx used by other brands, so Merrell loses a bit of leverage to other super lightweight competitors like Acr’teryx, Salomon, and Nnormal.

The shoes are not wide per se, but the flexibility of the upper allows your foot to spread out. This is confusing because the front of the shoe comes to a defined point and yet it’s a comfy fit even for my wide feet and bunions.

The combination of different shades of oranges, black, and white with a long Merrell wordmark across the lateral aspect of the shoe makes it really stand out and passers-by won’t confuse it with anything from Hoka, Brooks, Salomon, or other companies.

Merrell MTL Skyfire 2 - lateral view

A lateral view of the Merrell MTL Skyfire 2.

Merrell MTL Skyfire 2 Midsole

The Merrell MTL Skyfire 2’s two-part, dual-density FloatPro Foam midsole is shockingly cushy despite the shoe’s overall stripped-down appearance. There’s an innovation in the form of its aforementioned FlexPlate, which feels much more propulsive and, better yet, less noticeable than other plated trail shoes on the market.

The plate is sandwiched between two layers of the very comfortable FloatPro Foam. The power transfer feels more defined than in, say, the Hoka Tecton X 2 — check out our Hoka Tecton X 2 review. However, the model’s 6-millimeter drop and extremely minimalistic design caused my shins to be very sore the day after my first run, having bombed down technical descents over about nine miles and 4,000 feet of gain and loss. This break-in period was brief, though, and my legs quickly adapted thereafter.

The insole is paper thin and after competing in this year’s almost entirely snowy Broken Arrow Skyrace Vertical Kilometer, where my socks and shoes were completely wet at the end, I took the shoe off and the insole had slipped all the way to the medial aspect of the shoe. Merrell might find future iterations of this series to forgo insoles altogether.

Merrell MTL Skyfire 2 - medial view

A medial view of the Merrell MTL Skyfire 2.

Merrell MTL Skyfire 2 Outsole

Earlier in this review I mentioned the upper material being less durable than shoe brands using Matryx. But where the brand exceeds some of its lightweight competitors in the Merrell MTL Skyfire 2 is in traction.

The superior traction comes from both the use of Vibram MegaGrip, really the industry standard when it comes to trail running shoe outsoles, as well as the unique honeycomb pattern of the outsole and its lug configuration.

In this day and age, the use of something like, say, Salomon’s Contagrip outsole, which no doubt affords less traction on a competitor shoe model, the Salomon S/Lab Pulsar 2 — here’s our Salomon S/Lab Pulsar 2 review if that’s of interest — is head scratching.

Lately for many athletes, Merrell has found a home alongside brands like VJ, which makes shoes used often by obstacle-course racers because of their mix of light weight and deep lugs that work in the variety of conditions that these athletes face: mud, rain, dirt, and support for leveraging obstacles.

This shoe is similar with 5-millimeter deep lugs, but the comparison beyond this to any VJ shoe I’ve tested is unfounded and the MTL Skyfire 2 vastly outperforms the Finnish company’s shoes.

The outsole wraps up to the front middle of the upper, and it unfortunately has begun peeling off the outsole.

Merrell MTL Skyfire 2 - outsole

The outsole of the Merrell MTL Skyfire 2.

Merrell MTL Skyfire 2 Overall Impressions

Though I found the break-in period a bit brutal simply from not having conditioned my shins, the Merrell MTL Skyfire 2 sits firmly atop my list of favorite trail racing shoes. Though moderate distances are probably best, the shoes are just a showstopper in terms of their combination of light weight and incredible traction.

Though upper durability hasn’t been perfect, being selective about this shoe’s use in time trials, vertical-kilometer races, short FKT attempts, and more makes it the perfect tool when speed is your concern.

You can also read our Best Lightweight Trail Running Shoes article, where we’ve named the Merrell MTL Skyfire 2 a top shoe in this category.

Shop the Men's Merrell MTL Skyfire 2Shop the Women's Merrell MTL Skyfire 2

Call for Comments

  • Have you been running in the Merrell MTL Skyfire 2? What do you think of the shoe overall as well as of its details?
  • Did you use the original MTL Skyfire? If so, what do you think about the substantial updates made to this second version?

[Editor’s Note: If you’re affiliated (i.e., an employee, ambassador, etc.) with a brand, please share your relation in each of your comments on this article. Thanks!]

Our Favorite Trail Running Shoes

Check out our Best Trail Running Shoes article to learn about our current favorite trail running shoes!

Merrell MTL Skyfire 2 - top view

A top view of the Merrell MTL Skyfire 2.

Craig Randall

Craig Randall is a Gear Editor and Buyer’s Guide Writer at iRunFar. Craig has been writing about trail running apparel and shoes, the sport of trail running, and fastest known times for four years. Aside from iRunFar, Craig Randall founded Outdoor Inventory, an e-commerce platform and environmentally-driven second-hand apparel business. Based in Boulder, Colorado, Craig Randall is a trail runner who has competed in races, personal projects, and FKTs.