Merrell MTL Skyfire 2 review: uber-light, grippy trail racer

In this Merrell MTL Skyfire 2 review, we’ll look at one of the flagship releases for 2023 from the renowned US outdoor brand, reviewing this technical trail running shoe’s design, features, performance and comfort.  

Merrell is a brand that has built its reputation firmly on its hiking heritage. Shoes like the Moab have helped generations of hikers get out there and explore the great outdoors, spawning a family of footwear, all built on the time-tested Moab platform. In more recent years, the brand has also sought to capitalise on the ‘fast-hiking’ trend by releasing lighter, more technical footwear such as the Moab Speed and Flight ranges and the MQM series of hybrid approach shoes (intended for ‘Moving Quickly through the Mountains’, which explains their acronym). 

Admittedly, they’ve also dabbled in dedicated trail running shoes, with models like the Nova, Long Sky and first-generation Skyfire. But it’s fair to say that the MTL Skyfire 2 represents the brand’s most ambitious and most technical runner yet. Developed in-house by the Merrell Test Lab – hence the ‘MTL’ designation – in close collaboration with Merrell’s roster of elite mountain athletes, the Skyfire 2 represents a landmark release for the brand. 

Merrell MTL Skyfire 2 review: price and release date

First released in SS23, the Merrell MTL Skyfire 2 comes in men’s and women’s fits, both priced at £170/ $200. The original colourway was a striking blaze orange and white, with a new orange/electric blue scheme plus a black, green and khaki 1TRL edition released for AW23. 

Merrell MTL Skyfire 2 review: specifications

• Sizes: Men’s UK 6.5-14, women’s 2.5-8.5
• Weight: 198g per shoes (Men’s UK 8)
• Lugs: 5mm
• Stack height and heel-to-toe drop: 25mm Heel/19mm Fore, 6mm drop
• Materials: BZM-8 rock plate and dual density FloatPro Foam midsole, Vibram MegaGrip outsole, NXT lined EVA footbed, breathable mesh and TPU upper. Vegan-friendly. Incorporates recycled materials (100% recycled laces, 100% recycled mesh footbed cover)

Merrell MTL Skyfire 2 review: design and features

The first thing you notice when you pick up the MTL Skyfire 2 is its weight – or lack of. This is a shoe for dedicated gram-counters. It is impressively light, with every element of the uppers, midsole and outsole engineered to keep the overall weight to an absolute minimum. As a result, it tips the scales at just 198g per shoe in a men’s UK 8. That makes this one of the lightest trail running shoes on the market.

In many ways, they look and feel a lot like a pair of track spikes. They’re fairly close-fitting, with superlight mesh uppers that hug the foot and a narrower toebox than is typical for most running shoes. The outsole is a Vibram Megagrip compound, and the tread pattern is a latticework of aggressive, chevron-shaped 5mm lugs interspersed with weight-saving cutaways. A raised heel counter cups the rear of the foot snugly, while a contoured, cutaway cuff ensures good freedom of movement and plenty of ankle flex, with no pressure on the talus or Achilles. 

Those uppers are cool and breathable, offering fantastic ventilation for the feet. They also drain well and dry quickly. This isn’t a waterproof shoe, so you will get wet feet in damp conditions, but the flip side is that these shoes will not get sodden or waterlogged. TPU overlays offer a little upper reinforcement, but overall foot protection is fairly minimal.

In terms of construction, the Skyfire 2 has a lightweight rock plate embedded in the midsole, which adds rigidity and offers some underfoot protection. It also aids stability by supporting your foot laterally, preventing the sole from torsional twisting. The plate is actually sandwiched between two layers of EVA foam in the midsole of differing densities, which provides plenty of bounce and impact absorption on landings and take-offs. The flex plate also helps to transfer kinetic energy into forward momentum, encouraging a faster cadence and a more natural, rhythmic stride. 

The shoe’s overall drop is 6mm, with a 25mm heel stack, so despite the lightweight construction, this is no minimalist, barefoot-style shoe. It offers a good balance of cushioning and responsiveness underfoot without feeling too spartan.

A recycled mesh footbed adds a little more comfort, and it’s also treated with Merrell’s NXT anti-bacterial lining, which should help to prevent odour build-up. Laces are made from recycled materials, with an unusual elastic tab lace keeper to prevent them from getting tangled or coming undone mid-stride. It’s a nice touch.

Merrell MTL Skyfire 2 review: performance and comfort

This is a fast-feeling shoe, thanks in large part to its lightweight build. We put them through their paces in the hills and mountains of Snowdonia, North Wales – taking on several trails in the renowned Coed y Brenin forest park, where dedicated running routes snake amongst downhill mountain bike tracks.

When climbing, the featherlight feel of these shoes certainly means they feel less leg-sapping compared to clunkier trail shoes. And on the more technical sections, consisting of steep switchback descents and narrow wooded paths threaded with tree roots, they performed well, delivering secure traction and plenty of precision, thanks to their neat toebox and low-profile design.

This is a shoe that demands concentration when it comes to foot placement though – the lack of all-round protection means that you do need to be careful with your landings. And though the rock plate absorbs some impacts underfoot, they’re less well suited to particularly broken, rocky and uneven ground. Still, that makes for very focused running, which is not necessarily a bad thing.

They also proved very comfortable in runs of up to half-marathon distances. But given that the Skyfire 2 is built for performance and speed over outright durability, this is really a shoe that we’d recommend saving for race days and other trail runs where you’re really aiming to push the pace. In that sense, it’s not really a ‘quiver of one’ shoe – you’ll probably want to team it with a more forgiving shoe for everyday use or relaxed training runs.

Think of it as a thoroughbred racer rather than an all-round workhorse. That way, you’ll extract maximum value from them when it counts rather than burning through them too quickly. Because ultimately, the lattice outsole means there’s a lot of exposed foam underfoot, while the mesh uppers will inevitably wear through quicker than burlier shoes. If we were looking for weaknesses, it would be in this area, as we would question the Skyfire 2’s outright durability if subjected to too much punishment. Then again, that is the almost inevitable price you pay for such low weight. 

Merrell MTL Skyfire 2 review: verdict

There's no denying that this is something of a specialist shoe. But as a superlight trail running shoe for race days, Merrell's MTL Skyfire 2 is one of the best options. In that sense, it excels in its design specification – it's unbelievably light on the feet, comfortable yet responsive over distances of up to a half-marathon, and out-grips most of its similarly lightweight rivals. On the other hand, as an all-around trail running shoe, it wouldn't be our first choice unless low weight is your ultimate priority. Our advice? Save it for the days you really want to push the pace or beat the competition.

Merrell MTL Skyfire 2 review: Alternatives to consider

If you’re after a similarly superlight trail running shoe, then the Merrell MTL Skyfire 2 competes squarely with rivals like the Salomon S/Lab Pulsar 2, the Arc’teryx Norvan SL 3, the Adidas Terrex Speed Ultra and fell-running favourite, the Inov-8 X-Talon G 210.

All use similar ultralight uppers and come in at less than 250g per shoe. However, we reckon the Skyfire 2 outgrips its Salomon, Arc’teryx and Adidas Terrex rivals on most terrain, though probably comes second to the mega 8mm lugs of the Inov-8 X-Talon. On the other hand, that’s a dedicated fell-racing shoe that works best on soft and sloppy ground, so it lacks the cross-terrain versatility of the Skyfire 2.

If you want similar characteristics but can sacrifice a little extra weight for the sake of added cushioning, then popular alternatives include the Hoka Zinal 2 as well as the Mafate Speed 4. Both are excellent trail running/racing shoes that promise slightly superior long-term durability and will also feel more forgiving underfoot over longer distances.