Mammut Mercury IV Mid GTX review: the premium boot that undercuts our editor's pick

The Mammut Mercury IV Mid GTX is the premium pick in our boots lineup, and it earns that slot in an unusual way: by costing less than the boot above it. This is a mid-cut GORE-TEX hiking boot from the Swiss alpine brand, priced at £120 to £140 on Amazon depending on colour and size, which puts it comfortably under the £155 Salomon X Ultra 360 Leather Mid GTX that holds our editor's pick spot.

Around 1,200 Amazon buyers have reviewed it, and the pattern in that feedback is clear: high quality, comfortable, lightweight, and waterproofing that actually keeps feet dry in rain. There are two caveats to work through, a split verdict on durability and sizing that runs slightly small for some, and this review covers both. But as a serious-money boot from a serious brand at a price that undercuts its closest rival, the Mercury IV makes a strong case.

Where it sits in our lineup

Our best hiking boots guide covers everything from budget boots to the Salomon at the top. The Mercury IV slots into the premium end of that range as the Mammut answer to the question most readers at this price point are asking: if I'm spending proper money on a boot, what do I get for it?

What you get here is the badge and build philosophy of a Swiss alpine brand, a GORE-TEX membrane rather than an own-brand waterproof lining, and a mid-cut design that gives ankle coverage a low shoe can't. Mammut kit has featured across Coast & Fell for a while now, and the pattern with the brand is consistent: gear built to alpine standards that ends up overqualified for most British days out. That is precisely the kind of overqualification you want in a boot.

For the full picture on the brand, the technology and where the range fits, read our Mammut brand review.

Who the Mercury IV is for

This is a boot for hikers who have outgrown the budget bracket and want a proper mid-cut waterproof boot without pushing past £150. If your walking is UK day hiking, the Jurassic Coast, the South Downs, the Brecon Beacons in three-season conditions, a boot in this class covers all of it: waterproofing for the wet months, ankle coverage for uneven ground, and enough quality in the build that the boot disappears on your foot rather than announcing itself with every step.

The lightweight character that comes through repeatedly in the customer feedback matters here. A heavy boot taxes you over a long day in a way you don't notice until the final few kilometres. Buyers consistently describe the Mercury IV as light and comfortable, which is exactly the combination that makes a boot wearable for a full day rather than tolerable for a half day.

Who is it not for? If you already own a capable waterproof mid and it's working, there's no case for switching. And if your feet run wide or you're fussy about fit, read the sizing section below before ordering, because the feedback there is mixed.

What 1,200 buyers say

With around 1,200 reviews on Amazon, there's enough volume here to trust the patterns rather than the outliers. The summary of that customer feedback is worth quoting in full: customers find these hiking boots to be of high quality, comfortable, and lightweight, with good waterproofing that keeps feet dry in rain. They appreciate the fit, with one customer noting ample space around the toe area, and consider them good value for money.

Four things stand out in that. Quality, comfort, weight and waterproofing are the four attributes that matter most in a hiking boot, and all four come through positively. "Good value for money" appearing in feedback on a boot at this price is also telling. Buyers who spend £120 to £140 on footwear are not an easily pleased group, and value complaints are usually the first thing to surface when a premium product disappoints. They haven't.

The two areas where the feedback splits are durability and sizing, and both get their own sections below because they deserve more than a passing mention.

Waterproofing

The GTX in the name means a genuine GORE-TEX membrane, not an own-brand lining, and that distinction matters. GORE-TEX is the benchmark waterproof membrane in outdoor footwear for a reason, and it's the same technology doing the work in the Salomon X Ultra 360 at the top of our lineup.

The customer feedback backs the membrane up: good waterproofing that keeps feet dry in rain is one of the most consistent themes across those 1,200 reviews. For UK walking that's the test that counts. Not a lab spec, but whether feet stay dry through the persistent, soaking conditions that British trails serve up from October through April.

The usual limit of any mid-cut boot applies. The membrane protects you to the height of the collar and no further, so water deeper than the ankle cuff comes in over the top. That's true of every boot in this class, including the Salomon, and it's a reason to plan stream crossings rather than a mark against the Mercury IV.

Fit and sizing

The fit feedback is broadly positive. Buyers appreciate how the boot holds the foot, and one customer specifically noted ample space around the toe area, which is good news for anyone who wants room for toes to splay on long descents, or who pairs their boots with thick merino hiking socks in winter.

Sizing is where the feedback splits. Some buyers find the Mercury IV true to size, while others report it running slightly small. That's a common pattern with European alpine brands, and the practical advice is straightforward: if you're between sizes, or you know your feet sit at the larger end of your usual size, going up a half size is the safer bet. If you're buying on Amazon, order early enough that you can exchange if the first pair doesn't fit, and try them indoors before committing them to a muddy trail.

The durability question

This is the caveat that stops the Mercury IV taking the editor's pick spot, so it deserves a straight treatment. The durability feedback is split: some customers say the boots last well, while others report them falling apart after light duty use.

A split like that across 1,200 reviews usually points to inconsistency rather than a fundamental design flaw. If the boot failed as a rule, the overall feedback wouldn't describe it as high quality and good value, and it does. But "falling apart after light duty use" is a serious complaint when it does happen, and it happens often enough to appear in the pattern.

The practical response is to inspect a new pair carefully in the first weeks of ownership, keep your proof of purchase, and take up any early failure with the retailer promptly rather than pushing on and hoping. Early failures are the easiest kind to resolve, and they're a very different problem from a boot that wears out honestly after years of miles.

Weigh it against the Salomon on this point: our editor's pick has a season of real use behind it on this site with no build concerns, and that proven consistency is part of what the extra £15 to £35 buys.

Price and where to buy

The Mercury IV Mid GTX runs £120 to £140 on Amazon depending on the colour and size you pick, with multiple colours and sizes available. You can also buy direct from Mammut, but Amazon is currently the cheaper route, which is why it's our primary link.

That pricing is the heart of the Mercury IV's case. The premium mid-cut GORE-TEX bracket in the UK generally starts around £150 and climbs quickly. Getting a Mammut boot with a genuine GORE-TEX membrane under that line, sometimes well under it at £120, changes the value calculation for anyone shopping at the top of the market.

How it compares to the Salomon X Ultra 360 Leather Mid GTX

These are the two serious-money choices in our boots lineup, and the decision between them is the one most readers at this level are actually making.

Both are mid-cut boots with genuine GORE-TEX membranes from top-tier outdoor brands. The Salomon X Ultra 360 Leather Mid GTX is our editor's pick at around £155: it has a full season of use behind it on this site, from Pen y Fan in January to soaked Purbeck paths, and it has been faultless through all of it. That first-hand track record is why it holds the top spot.

The Mercury IV's counter-argument is price and pedigree. At £120 to £140 it comes in £15 to £35 under the Salomon, it carries the badge of a Swiss alpine brand, and its 1,200 Amazon reviews praise the same qualities that make the Salomon good: comfort, low weight, quality and waterproofing that works.

The decision splits cleanly. If you want the boot with the proven track record and the money isn't the deciding factor, buy the Salomon. If you want premium-brand build and GORE-TEX waterproofing at the best price the top bracket offers, and you're comfortable checking a new pair over early per the durability section above, the Mercury IV is the smarter spend.

Verdict

The Mammut Mercury IV Mid GTX earns 4.5/5 and the premium pick slot in our boots lineup. The customer consensus across 1,200 Amazon reviews describes exactly what a premium hiking boot should be: high quality, comfortable, lightweight and properly waterproof. At £120 to £140 it undercuts every serious rival at the top of the market, including our own editor's pick.

The half point comes off for the split durability feedback and the sizing that runs small for some. Neither is a reason to walk away, both are reasons to buy attentively: consider a half size up if you're between sizes, and give a new pair a close look in its first weeks.

For the wider field, our best hiking boots UK guide covers every bracket, and the Mammut brand review has the full story on the brand behind this boot.

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