The REI Magma 10 mummy bag arrived at my house fresh from REI’s warehouse in a large cardboard box that was insanely light for it’s size. Go figure, it was a 2lb box but it was probably a 3 cubic foot box that it shipped in. It was light in comparison to any other box I’d received that month. Inside the box was a fluffed out sleeping bag in what looked similar to a laundry bag a kid uses in college. Mesh with a little bit of nylon and a drawstring. Inside that storage bag was the mummy bag and a stuff sack for use while packing the sleeping bag.
Everyone has Standards
The bag has a 10 degree temperature rating, it’s in the name — however the temperature rating is on the EN 13537 standard, a European rating system for sleeping bags meant to be a standardization of measurements in sleeping bags. It used to be that you could pretty much just put whatever you wanted for the temperature rating on sleeping bags without any sort of real standard.
The EN standard has four temperatures that are measured and make a difference. The temperatures are Upper Limit, Comfort, Lower Limit, and Extreme. The Upper Limit is the outside temperature at which an adult male can sleep in the bag without excessive perspiration. Excessive sweat makes pretty much everything uncomfortable but it will soak down and negate the warming capacity that the loft provides. The lower limit is the temperature an adult male can sleep for 8 hours comfortably without waking. That’s usually pretty subjective. The Goldilocks zone is the comfort rating.
The bag’s Comfort rating is 22F, the limit is 10F. This seems to be a bit of a advertising faux pas when you consider it’s being marketed as a 10 degree bag.
The outer layer of the bag is made with Pertex Quantum. A whatnow? It’s a windproof, soft, and lightweight material that if works as advertised allows the delicate insulation to provide full loft. This fabric also helps the bag become packable at an extremely light weight. The stuff-sack is made of the same material.
The fill of the REI Magma 10 Sleeping bag itself is 850-fill power down. The 850-fill means, at least in theory, that the down fill on the bag provides at least 850 cubic inches of loft. That’s a pretty fluffy sleeping bag.
The regular sized bag weighs in at 1lb 13oz, but in late 2018 when this bag went on sale they announced by way of reviews on REI.com that the regular length bag will be discontinued and they will only be selling the long bag from now on under the Magma line. The long bag can comfortable accomodate a 6 foot tall person, I’m 5’8″ or so without my hiking boots and have plenty of room in the foot box.
The bag is contoured to fit, and is somewhat of a slim mummy bag. I would say that if you have a significant beer belly, mine is only mini sized, consider trying it out at an REI retail store. Though their return policy is pretty good. The reasoning behind this is to keep the down around you, maximize the bag’s ability to pack and the heat retention. It’s good to have some air pockets around you, but if they’re cavernous they require heat, generated by you in order to bring the entire thing up to temperature while you’re sleeping. This in turn can lead to feeling somewhat claustrophobic, but people who’ve used mummy bags before will have no problem adapting to this fit.
Overall I think the REI Magma 10 is well constructed, light, and is a fairly cost effective option. The MSRP is $350 which means it’s not exactly a frugal option, but most backpacking kit comes at a price premium for being light and compact. I suggest you save one of your 20% member perks for this. The bag is better suited to warmer climates, as during our scouting trip for elk in August in the Colorado mountains it was still a little chilly — though that trip didn’t warrant a 0 degree bag.