Robust, comfy and versatile, the update to this alpine pack range retains its original close fit and handy chest pockets, features influenced by running vest design. It's this that really sells it, reckons Dan Bailey.

With their Trion range, Mammut were early adopters of the idea that climbing packs could benefit from the influence of running vests, in terms of a body-hugging low-profile harness, and stretchy shoulder pockets for easy on-the-go access to snacks, phone, and soft flasks. I'm increasingly of the opinion that most rucksacks would be better built along these lines, and would definitely count myself as a Trion fan ever since I tried one on (sorry).

The range has been updated for this year, and comes in a number of shapes and sizes, from the minimalist fast-and-light Trion 15, via a 28 and 38 - both good options for all-round use - to the gear-toting Trion 50, which looks like the one for backpacking, hut tours and extended mountaineering journeys.

We reviewed a previous model in this series some years ago, the Trion Nordwand 38, and found a lot to like. In fact it's been a firm favourite ever since, from year-round walking and summer mountain rock to winter mountaineering (it's a bit small for full-on Scottish winter climbing loads). The new 28 not only shares the looks, but also a lot of the features we got on so well with before, especially the well-vented back system and close-fitting shoulder straps that give a nod to running vest design. It's a smaller pack of course, and does without the lid pocket that larger models in the series offer. A few other details are new too.

What's it for?

Mammut describe the Trion as an alpine backpack, and I think they mean that quite broadly since it's equally useful for walking, climbing, and even ski touring. My old Trion 38 remains a regular year-round companion on the hills of Scotland. I find the body-hugging, unrestrictive fit great for scrambling and winter mountaineering, while the back system has the sort of airy feel you need for summer comfort.

It's light enough for your average generalist user - if not runners and serious weight watchers - but also sufficiently sturdy and supportive to carry heavier loads in comfort, be that a rope and rack in summer or axe, crampons and extra layers in winter. With its smaller volume the Trion 28 suits less gear-intensive trips, and I can see it being equally useful for summer alpinism, year-round hillwalking, or lightly-equipped Scottish mountaineering days in any season. It would be spot on for a summer Cuillin traverse, for example (fairly generous for a one-day outing, big enough for a bivvy if you're super-disciplined about packing light).

Weight and durability

At 1030g on the home scales (Mammut say 1000g) the Trion 28 is not really lightweight by modern standards, more a midweight perhaps. It's 40% bigger or so, but it weighs well over twice as much as Rab's Latok 20, for example, another running-vest-inspired climbing pack I reviewed recently. It's possible to shed 69g by removing the padded section of the hip belt (an option larger users in particular will probably want to take) and a further 122g if you take out the wire frame. Even still, the Trion might not be your first choice for genuinely weight-critical occasions, but in its favour offers that bit more support and comfort than an outright minimalist pack would be likely to.

It's really well made too. After a lot of use my old Trion 38 is still going strong, with no hint of wear or damage. Its burly ripstop fabric is really abrasion-resistant, and shrugs off rain well too, so while the seams and entries aren't water-resistant, and you've go to pack stuff in drybags in changeable UK conditions, the overall feel is a pack that can take plenty of abuse and a fair bit of weather.

Fit and comfort

Both a men's and a women's model are available, at a back length of 46cm and 43.5cm respectively. As with most climbing packs the Trion 28 has no adjustability, so it'll either fit you or it won't. It's a small pack and the back length is understandably pretty short, so at 183cm tall and with a fairly long back I'm way too big for the hipbelt to do its job - on me it's a belly belt. I detached the padded section of hip belt straight away, which leaves just a webbing band. This cannot be removed, but is easily wrapped around the pack if you don't want to use it - I generally wouldn't on a rucksack this small, though perhaps it does marginally help to stabilise things.

For load-carrying support Mammut have included a light wire frame, and I don't think it's worth removing this since it makes for a comfier feel. A foam back sheet protects you from jutting items in the pack, while the additional padding is sensibly minimalist and really airy for hot weather comfort. Arm movement is unrestricted, courtesy of nicely sculpted shoulder straps; these have padding only over the shoulders - the weight-bearing part - while down over the chest it's a broad mesh strap, which hugs the body in the way a running vest does, for a close fit and maximum breathability. Again, like a running vest, the chest clip is on elastic, which is supportive enough to hold everything firm while also feeling comfy and forgiving.

Overall, and bearing in mind it's too short on me for the hipbelt to work as intended, I find the close fit of the Trion 28 hard to fault. It's supportive enough when walking with a heavy pack, and offers unrestricted movement when climbing or scrambling. By the standards of a climbing pack it's really well vented too. I think key to its success is the running vest influence. This is the main reason I keep returning to the old Trion 38, and so far I'm equally happy with the new version.

Features

As noted, this is a lidless design, so if you want a lid pocket (I do tend to use them a lot) then go for a Trion 38 or 50. Closure is via a rolltop, with an additional zip - the point of which is presumably to allow you to stuff things right to the gunwales. You get a top rope strap too, which given the limited internal space is likely to see a lot of use.

Mammut have added a side zip, so you can access the contents of the pack without fiddling with the rolltop. I'm sceptical of side zips on smaller packs, and think they're really only becoming useful at trekking pack size. On a 28L bag I definitely consider this surplus to my needs since it's really no big deal to root around from the top. The side zip is just something I might forget to leave closed, or a handy way for rain to get in. Naturally they have their fans, and perhaps you're one of them.

Inside is one small mesh valuables pocket with a key clip, plus the usual water bladder sleeve. For skiers there's an additional zipped compartment to stow avalance equipment; for other purposes, this might be a place to slip a map or a light shell. The stretchy chest pockets are the big plus for me, and I use them every time I'm out, for on-the-move access to snacks, phone and drinks. At a squeeze they'll just hold a 500ml soft flask though ideally they could be a couple of centimetres deeper, so I more often go with a 250ml bottle.

Daisychains give you extra places to clip things, while the axe and pole attachments are nice and simple. The addition of reinforced loops for skis increases the Trion's all-mountain versatility. For attaching a roll mat or suchlike the compression straps are usefully long, and can be wrapped around the pack to allow you to carry bulky items on the back as well as at the sides. My one issue with these is that there's no really neat way to secure the lengthy tails of webbing, which tend to hang loose and flap around in the wind; the Trion is quite 'strappy'.

Ethics and environment

Environmental credentials are pretty solid: The Trion is made primarily of recycled materials, and features a PFC-free DWR. It's also Bluesign and Fair Wear-certified.