Kelty Cosmic Ultra 20F sleeping bag review: cosy comfort for three seasons

The Kelty Cosmic Ultra 20° 800F sleeping bag (also referred to as the Cosmic Ultra 20F (RRP GBP £174.95 / from USD $199.95) is a warmer, lighter version of Kelty's popular Cosmic bags, and launched in 2021 in men's and women's versions. The 'Ultra' in the new model's name comes from what Kelty describes as 'ultralight but ultrawarm' down filling that claims to keep you cosy down to -7C. So how low could this bag really go on test? And is it warm enough, or light enough, to join our best sleeping bag or best lightweight sleeping bag rankings? Read on for our full Kelty Cosmic Ultra 20F review.

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Kelty Cosmic Ultra sleeping bag review: design and features 

Down-filled sleeping bags tend to really deliver on comfort and warmth, and Kelty's Cosmic Ultra is no exception. Its silky outer material is stuffed with insulating DriDrown, Kelty's own-brand technology which, as the name suggests, is designed to keep you warm without excess weight but will still work well if it gets wet from rain or humidity. 

At 1.09kg this isn't the lightest or most portable sleeping bag on the market, and is a tad too bulky for lightweight adventuring, but it isn't prohibitively heavy or bulky, and will fit into a bigger backpack – perfect for weekends outdoors or more casual wild camping as well as for traditional camping trips. 

The Cosmic Ultra is marketed as a three-season bag – the '20F' in its name depicts the temperature rating in Fahrenheit of this all-American-designed bag, which translates to -7C, and thus is suitable for most seasons in the UK. If you do want a bag that can tackle the coldest winter conditions, Kelty also makes the Cosmic Ultra 0F version of this bag, designed to go comfortably down to -18C.

Kelty has kept an eye on environmentally-friendly construction here, too, creating a water-resistant fabric that doesn't use PFC (a group of harmful chemicals often used in outdoor kit as a waterproofing agent). 

Kelty Cosmic Ultra sleeping bag review: performance and comfort

Climb into the Cosmic Ultra at camp and you'll instantly be cocooned in warmth. We liked the bag's mummy shape, which traps in body heat quickly, the silky-soft nylon lining, which is very comfy against the skin, and the handy zipped inner pocket, ideal for stashing your phone or your head torch. A draft collar around the neck also helps keep you cosy in the night, even if you don't want to cinch the hood around your head too tightly. While we couldn't check out its claims of comfort down to -7C, we tested the bag out in chilly spring conditions when the temperature dropped to 2-3C and felt comfortably warm – we'd recommend using it from spring through to autumn and for winter use in the UK if you're not heading into more extreme mountain conditions.

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Size matters – the unisex Cosmic Ultra 20F bag is 198cm in length and should suit most taller campers. On the petite side? A women's version is available – our 5'7 tester reckoned this female-specific design would suit anyone up to 5'7, but if you like a roomier sleeping bag, especially around the torso, the unisex bag might still suit you better.

We'd only really flag up one thing after a few weeks of testing out this bag – for the first few times you use it, the Kelty Cosmic Ultra has a slightly unpleasant synthetic smell. This does fade, and we found that leaving it in the sun for an hour or two helped, so we don't think this niggle would put us off buying what is otherwise a high-performing bag. 

Kelty Cosmic Ultra sleeping bag review: verdict

Kelty's motto is 'Built For Play', and we reckon its Cosmic Ultra is ideal for good times in the outdoors in most seasons. Reliable warmth, resistance to water and great comfort make this a solid choice if you're after a down-filled bag. This design offers great value for money, standing up on test when compared to bags available at twice its price point. The option to pick a female fit is the cherry on the cake.