REVIEW: Crux RK40 Rucksack

The crux RK40 is one of the new generation of roll-top rucksacks, a simple, light yet bombproof sack suitable for everything from evenings at the crag to multi-day alpine missions. With an RRP of £179 there is no escaping the fact that this is one of the more expensive sacks on the market for its size, but in my opinion the build quality and durability make up for this. Crux have developed a reputation in recent years for making minimalist, functional, well-constructed gear, and this sack lives up to expectations. The sack’s compression system will not be to everyone’s taste, but this can be easily removed for outings on which it is not needed.

A superb minimalist (but not too minimalist) alpine and winter sack, 138 kb
A superb minimalist (but not too minimalist) alpine and winter sack
© Will Harris


40l is a good size for winter climbing, winter hillwalking and multi-day Alpine outings. Whilst it’s possible to go all French mountain guide and cram your gear into a 25l sack, and indeed this is preferable when tearing up single day Alpine objectives, this approach has its limitations. I think that a winter rucksack needs to swallow extra warm clothing, rack and rope, meaning that your gear isn’t sodden by the time you have fought the elements on the way to the crag. The RK40 happily accepts a winter load, and equally serves well for longer Alpine objectives. I used it for a three-day trip in to the Salbit in Switzerland, and was happy with the way it carried rope, rack, clothing and snacks up to the hut, but then felt light and unrestrictive when carried on multi-pitch rock routes.

Packed for a multi-day Alpine rock trip , 224 kb
Packed for a multi-day Alpine rock trip
© Will Harris

"It is possible to go too far and end up sacrificing function in order to save weight, and I would argue that a balance must be struck between durability and weight-saving. I think that the RX-40 finds this balance well"


The simple roll top works well, and is easy to use whilst wearing gloves. The lack of additional drawstring or lid makes getting into the pack quick and easy, speeding up transitions. The slightly outward-tapering shape of the main compartment makes it easy to shove gear into the pack, but is small enough to prevent it from feeling top-heavy when fully loaded.

The small externally opening pocket tucked into the neck of the bag works well. My only comment here would be that it can be difficult to remove items from this pocket when the rucksack is fully loaded, as the pocket can be squashed by the contents of the main compartment.

Structure, straps, and carry comfort

I found the pack to carry comfortably when fully loaded. There is the option to add two tubular titanium stays (sold separately) to improve the carry when carting heavier loads, but with the type of weights likely to be transported when alpine or winter climbing these seemed unnecessary. The waist strap is made from simple webbing which sits well. The RK40 shares the same tried and tested shoulder straps and back as other crux rucksacks, a simple yet comfortable system which seems to work well.

Axe attachment - simple but effective, 99 kb
Axe attachment - simple but effective
© Will Harris

Back system - simple but comfy, 86 kb
Back system - simple but comfy
© Will Harris

Perhaps the most striking feature of the rucksack are the corset-like compression straps running down its sides. These allow the capacity of the sack to be pulled in, presumably to make the bag smaller to climb with when it is emptier. This works in making the sack feel very manageable when climbing, but I found it comfortable to climb with even when uncompressed. I’d describe the look of these compression straps as a little marmite, with strong opinions both for and against their striking appearance. For some, the compression straps might detract from the sack's otherwise clean, simple lines, and luckily for these people the cord running through the compression points can be easily removed. The cords do however double up as useful external storage, for a roll mat for instance. A lower pair of compression straps is good for carrying skis, though I think that trying to fit skis also into the crisscross cords could be a bit of a faff.

The RK40 features a top strap too, which acts to both hold the sealed roll-top neatly in place and to attach a rope to the outside of the pack. This strap has to be fastened regardless of whether carrying a rope or not, to prevent it from sitting between the bag and the carrier's back. This perhaps adds a couple of seconds of extra faff, but the added capacity to carry a rope on the outside of the bag makes this slight inconvenience well worthwhile. A nice touch, the casing for the buckles on both the roll top and the rope carrying strap are made from a lightweight metal, reinforcing this potential weak point.

A good solid load carrier from bouldering..., 197 kb
A good solid load carrier from bouldering...
© Will Harris Alpine climbing, 79 kb Alpine climbing
© Will Harris

Fabric, Build Quality and weight

The rucksack seems to stand up to abuse well. Made from tough yet lightweight Cordura and Kevlar, complete with fully welded seams, in my experience to date the sack lives up to its claim of being waterproof. On first acquaintance it feels well made, as you would expect for a rucksack with a £179 price tag, and more importantly this impression has remained as the sack has stood up to all of the abuse that I have thrown at it. I would say that it is the durability of the materials used that justify the hefty price tag, as the bag feels like it will last for the long haul.

Rucksacks have not escaped the fetish for lightweight gear in alpine climbing, and with good reason. The extra grams add up to make hard work, and as the Americans say, ounces make pounds and pounds make pain. That said, it is possible to go too far and end up sacrificing function in order to save weight, and I would argue that a balance must be struck between durability and weight-saving. I think that the RX-40 finds this balance well. At 995g it is pretty light when compared with other products of a similar capacity, yet in reaching this weight it doesn’t seem to have compromised function or durability.


Metal-reinforced buckles and axe toggles, 110 kb
Metal-reinforced buckles and axe toggles
© Will Harris

Side compression straps, 113 kb
Side compression straps
© Will Harris

The RK40 has simple metal toggles designed to fit through the hole often found in the head of modern ice axes. Coupled with elastic attachment points to hold axe shafts in place, this system allows two technical tools to be easily attached. Alternatively, ice axes can be slotted into the compression straps on the side of the sack.


A simple, light and bombproof rucksack, the RK40 is certainly not a budget option, but sometimes you get what you pay for. Whilst the compression straps won’t be to everyone’s tastes I don’t think that they detract from what is in essence a great mountain pack. Since starting to test the RK40 it has been everywhere with me, from cragging to multi-day Alpine trips, and whilst I will keep a 30l sack handy for single day Alpine routes I can see the RK40 serving as my go-to sack in more or less every other setting. With this build quality, I’m looking forward to using it for a long time to come - be that on longer Alpine routes, for winter climbing or even on overnight backpacking walks or hut-to-hut tours.

What Crux say:

The RK40 is an exceptionally tough pack, ideal for technical routes that involve hauling and necessary physical abuse. It is equally at home in very wet activities, with the roll-top closure and fully welded construction fully adept at keeping out water. Although frameless, it has frame-sleeves to allow the addition of optional frame-stays for better carrying.

It is completely waterproof and made from a rugged PU-coated Kevlar/Cordura fabric. At home on either rock or ice routes, this is a versatile, easy loading and easy handling sack.

  • Capacity: 40l
  • Weight: 995g
  • Colours: Red / Gunmetal
  • Roll-top closure system
  • Side compression cords and low side compression straps enable skis to be carried
  • Oversized back haul loop - easy to grab and clip
  • Two ice-axe holders
  • Small external pocket

For more info see

Crux RK40 prod shot, 57 kb

UKC Articles and Gear Reviews by Will Harris

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