Whether you use it as a small-ish trekking pack or a large alpine pack, the Trion Spine 50 (women's fit version: Trea Spine) combines a robust build, a mountain-oriented feature set, and a supportive and adjustable back system, to give you a pack that's well suited to short backpacking trips, UK winter hills, alpine hut tours and the like. This is no lightweight, to put it mildly, and a lot better for hiking and classic mountaineering than sustained steep climbing, but if you need a pack to carry hefty loads over long distances in comfort, and one that feels like it's made to take the knocks, then the Trion Spine very emphatically ticks the boxes.

Size, capacity and uses

On their website Mammut list the Trion Spine as both a mountaineering pack and a trekking pack, and that's a fair summary of its role with a foot in both camps. It's too heavy, bulky and rigid for technical climbing though. If you're after something a bit more compact for alpine climbing, the Trion Spine 35 looks more the thing, while for longer backpacking trips a 75L version is also available.

The 50 litre volume of the middle sized entry in the range, the one that I've been reviewing, is ideal for mini backpacking trips of around a night or two, with a generous main compartment that easily swallows camping gear, food and spare clothing. I've also been using it as a spacious day pack for winter hillwalking, and though it's on the large side for this I don't find it excessive when you consider the additional bulk and weight of winter gear - plus camera equipment in my case.

Weight and build quality

Mammut's quoted weight of 2200g is spot on according to my bathroom scales. Be under no illusion: The Trion Spine 50 is a very heavy pack for its size, and it wouldn't be hard to find equivalent models of about half this weight. If that's the main concern when you're picking which rucksack to use then the Trion Spine would be unlikely to get a look-in, so ultralight backpackers and weight conscious climbers will need to look elsewhere.

At only a few hundred grams more, you may feel the Trion Spine 75 has a better weight:capacity ratio. So why buy the 50? Well there's more to a pack than its weight alone, and in some other key respects this one does very well. Fit, comfort and load carrying support are top of the class, for instance; I'll look at these below.

It's also worth noting that with the weight come exemplary build quality, and robust materials. While Mammut don't give a weight for the fabrics, the ripstop polyamide that most of the pack is made from is really thick stuff, as is the textured fabric of the base and side panels. The overall feel is really durable, bucking the light-but-flimsy trend to give you a pack that is very clearly made to last.

Fit, comfort and support

A female-fitting version, the Trea Spine, is also available. For load carrying support the Trion is built around a substantial internal frame, but while this adds rigidity to the pack itself the carrying system allows the wearer a lot of freedom of movement. Consisting of a pivoting hip belt and a separate pivoting shoulder pad, connected by a stretchy fabric back panel, Mammut's Active Spine Technology allows the harness to flex in sync with your hips and shoulders as your body moves and twists when walking, allowing you to feel less restricted and better balanced than will often be the case with a heavy trekking pack. Pivoting carrying systems are nothing new of course, but this one seems particularly effective, while at the same time not being at all bulky or complicated. It just quietly does its job.

Padding is good and firm on the hip belt and shoulder straps, and the latter are heavily contoured to hug the body while allowing free arm movement. Between hips and shoulders only three 'islands' of padding (for want of a better word) are in direct contact with your back, while the rest is an airy mesh. There's plenty of air flow for comfort in warmer conditions, but not so much of a gap between the person and the pack as you'll find on some walking-oriented models, so the centre of gravity is still pretty close to the body, which helps with balance when you're clambering around on uneven ground.

Instead of offering the pack in different back lengths Mammut have made it adjustable for size, with a back length ranging from 46 - 51cm (the women's Trea Spine ranges from 43.5-48.5cm). At 183cm tall and with a fairly long back I am at the maximum extension, so I suspect anyone much taller than me is unlikely to get an optimum fit. The length adjustment, via a simple pull tab, could hardly be smoother or easier.

Overall the back system is one of the Trion Spine's major selling points, successfully transferring weight onto the hips and offering a well-balanced, comfortable and unrestrictive feel. At the sort of weights you'll be likely to carry in a 50 litre pack I don't think I've used many better; and I suspect it will prove equally effective on the 75 litre version of this pack. Top marks to Mammut here.

Features

Primary access to the pack is via a conventional lid with buckles and drawstring, with an under-lid rope retaining strap. The lid can be raised to accommodate oversized loads, and can also be easily removed (though you're not going to save much weight by doing so since the Trion Spine will never be a minimalist). For your bits and bobs there's a reasonable-sized (but not massive) over-lid pocket with a non-water resistant zip. You get no under-lid pocket, but small valuables can go in a little zipped mesh pocket just inside the pack, and this has a key clip. One criticism of the lid shape is that it doesn't form a proper seal over the top of the pack when you're stuffed right to the max - fine in dry weather, but less so in the rain.

A huge wrap-around zipped flap gives you a second entry, to access stuff buried deep down without having to unpack it all through the top of the pack. While a lower zipped entry makes sense on a larger trekking pack, I've never been convinced by their usefulness on day packs, and since the Trion Spine 50 straddles that backpacking/day pack boundary I find it a borderline feature here. In its favour the zip is chunky and robust, and I know some folk like to get at their gear this way. On the other hand any zip is a potential point of failure; this one makes no attempt to be water resistant and so will inevitably let in the rain; it adds a small amount of weight and complication; and should you ever leave it undone by mistake then you'd risk losing things. On balance I would prefer not to have it, and am unlikely ever to use it, but others will form their own opinion. Inside the zipped flap you get a secondary zipped sleeve, into which you could stuff a jacket. I'm not convinced by this feature either, since you have to open the main zip to get at it, and using it takes up space inside the pack rather than adding capacity.

For easy access to bits and bobs on the go, there's a zipped pocket on one side of the hip belt, and another on one of the shoulder straps. I find both a bit small; the former could do with being stretchy, since it's not much use for anything more than a couple of cereal bars, while the latter is just too narrow for my smartphone (an iPhone 6, so not huge). On the other side of the hip belt you get a gear loop. Two robust daisychains down the front of the pack provide places to clip stuff on, while the twin side compression straps are usefully long if you want to attach a tent or a foam mat, and can also be looped around the front of the pack to attach something extra-bulky. All straps and stitching feel really strong, and the webbing straps feature elastic loops to neaten any spare tails.

Combining both a webbing loop and a clip at the head end (which gives you two axe attachment options) and velcro retainers for the shafts, the axe carrying system is robust and simple, two points to its credit. A minor downside is that the velcro loops are quite easily removable, and you need to be careful not to lose them when taking axes off the pack. Poles can also be attached here, but it would have been nice to have some sort of socket to securely hold their tips.

You get very tough side ski attachment loops at the bottom of the pack, which skiers will welcome. Personally, however, I'd have liked to see pole sleeves too, since these are a good place to hold both trekking poles and a water bottle, neither of which can be securely stored on the sides of the Trion Spine. I'm sure more people will use this pack for walking than skiing, or indeed climbing - certainly so in the UK - so this is a bit of an omission.

Other features include a robust carry loop, a hydration sleeve, and a sternum strap which features an inbuilt whistle, and slides smoothly up and down the shoulder straps to adjust for height.

Summary

The Trion Spine combines exemplary carrying comfort with the durability to take a lot of knocks, and while it is very heavy I think that is understandable considering the substantial pack that you're getting. You could consider its hefty price tag an investment on a pack that promises years of service. Though it has some of the character of a climbing pack, it's a lot better suited to classic mountaineering journeys than anything steep and technical, for which it is way too heavy and rigid. For me its primary use would be tougher backpacking trips, such as multiple days on Scottish Munros. There's a lot to like here, and the back system is one of the best I've used. But at over 2kg, and £250, it's a purchase to weigh carefully.