Rab Muon 50L Hiking Pack Review

Overview

The Rab Muon 50L is a framed backpacking pack built around a running-vest-inspired harness, aimed at hikers and fastpackers who want a traditional pack’s support without the traditional pack’s bulk. It splits the difference between mainstream backpacking packs (think Osprey, Deuter) and true ultralight frameless designs — you get a real aluminum stay, a padded hipbelt, and 50L of capacity for right around 1kg. It’s best suited to lightweight overnight and multi-day trips where you’re not routinely hauling more than 25-30 lbs.

Key Specs

Spec	Detail
Weight	995 g (2.2 lb)
Volume	50 L
Dimensions	75 x 35 x 30 cm
Back length	48 cm (one size, “Medium,” not adjustable)
Material	100D (85% recycled) high tenacity nylon with Spectra ripstop
Back system	TRI-FLEX™ (aluminum frame + padded panel)
Hydration compatibility	3L bladder sleeve, dual exit
Carry features	Removable lid, trekking pole carry, compression straps

Performance

Carry & harness. The headline feature here is genuinely the harness, and reviewers agree. There’s a lot to like about the Muon, and what really makes it stand out is the shoulder harness, which has clearly been influenced - for the better - by running vest design. That translates directly to how the pack moves with you: one long-term user found it does fantastic with trail running, providing minimal bounce and sway thanks to that chest vest, barely adding much mass while giving much more stability and load distribution with the frame. UKC’s tester summed up the overall feel well: lightweight, comfy, well-vented, and with plenty of features.

Weight-to-feature ratio. For a 50L pack with a real frame, sub-1kg is a good number. One reviewer put it plainly: a kilogram for a full framed, fully featured backpacking rucksack is spot on, and although the Muon is only 50 litres it fits the bill. TreeLineBackpacker echoed that sentiment, calling it an excellent balance between mass, durability and packed size, with all the necessary and nice to have features, without splurging on unnecessary features or cutting weight on things like durability.

Durability. Multiple testers independently praised the fabric. Ultralight Outdoor Gear noted they were very impressed with the fabric strength at this weight — it doesn’t feel like it’s going to let you down, although the side mounted stretch mesh pockets look like a longer-term weak area. A long-term owner who’s used the pack for backpacking, paragliding, and skiing with loads up to 40 lbs found the fabric tough, standard ripstop/gridstop nylon that he’s sure will last a long time, though stitching is slowly showing signs of wear. Worth noting: it’s not waterproof and you will want a waterproof pack cover if you anticipate more than a drizzle of rain.

Fit. This is a one-size-fits-most pack, and that’s a real limitation. As UOG pointed out, the Muon only comes in one size, so it’s worth knowing or measuring your back-length to make sure this is a contender — Rab refers to it as Medium (19”/48cm) and doesn’t specify a range of back lengths it’s designed for. TGO Magazine flagged the same issue as a downside: the non-adjustable back only comes in one length, and a few design niggles make it less than perfect. If you’re notably shorter or taller than average, try this on before buying — it’s not a pack you can dial in with a torso-length adjustment.

Water bottle pockets — the recurring complaint. This is the single biggest gripe across reviews. One user was blunt about it: the side pockets are the Rab Muon 50’s one glaring flaw — the freaking water bottle slots, which is, in fact, absolutely not fine. His bottle fell out repeatedly during normal use, from bending over to loading the pack into an overhead bin, and he ended up rigging a carabiner tether so a dropped bottle would dangle rather than roll away. UOG’s reviewer had a related complaint about accessibility: without hipbelt pockets, they ended up storing small items such as a compass in the water bottle pocket, and there’s a danger that when reaching for a jacket you inadvertently drop the compass.

Chest strap system. The cordage-based chest strap that ties into the running-vest aesthetic is comfortable but fiddly. One tester noted: while I like the chest strap design for its comfort and adjustability, it also comes with some quirks — the clips can be a little finicky to get into place, as they’re small hooks that connect onto corded loops that stay in place via tension, occasionally popping loose on one side while you’re clipping the other.

Pros & Cons

Pros

• Genuinely comfortable, running-vest-inspired harness that keeps the load stable and close to the body, even for faster-paced movement or light scrambling
• Sub-1kg weight for a fully framed 50L pack with real support
• Tough, abrasion-resistant fabric that testers trust for the long haul
• Removable lid saves weight when you want to go minimal
• Generous, stretchy side pockets that swallow more than just a water bottle

Cons

• One back length only, non-adjustable — fit isn’t guaranteed for everyone
• Side water bottle pockets are widely reported to let bottles fall out during normal handling
• No hipbelt pockets, which pushes small essentials into those same unreliable side pockets
• Fiddly cord-and-hook chest strap clips that can disconnect unevenly
• Not waterproof; pair with a pack cover or liner for wet conditions

Who Should Buy This

The Muon 50L makes the most sense for hikers and fastpackers who want a framed pack’s stability and load transfer without carrying a heavier mainstream design — think weekend backpacking trips, scrambling routes, or multi-day treks where you’re keeping your base weight down but still want real hip and shoulder support. If your back length is close to that 48cm Medium fit and you’re willing to work around the water bottle pocket quirk (a carabiner tether is a cheap fix), this pack rewards you with genuinely excellent carry comfort at a very competitive weight.

Verdict

The Muon 50L delivers on its main promise — a running-vest-style harness that makes a sub-1kg, fully framed 50L pack feel remarkably stable and comfortable on the move. The fixed back length and that persistently annoying water bottle pocket design keep it from being a slam dunk, but neither is a dealbreaker if you try the pack on first and rig a simple bottle tether. I’d put this at a 7.5/10: a well-executed, slightly quirky pack that’s worth serious consideration if the fit works for you.