Three-season down bags for backpacking and bothies. Compared on real ISO comfort ratings, fill power and the weight you will carry up the hill.
16 products, lightest first
Summer ultralight#1Mountain Equipment
Mountain Equipment's lightest bag at 420 g, rated comfort 16 °C for summer trips, from £150.
From
£149.96
at Alpinetrek
11 photosUltralight down#2Rab
500 g of 900 FP hydrophobic down, ISO comfort 5 °C / limit 0 °C, packing to 16 × 30 cm.
From
£399.95
at Cotswold Outdoor
8 photosLightest#3Sea to Summit
A 510 g summer-to-shoulder-season bag for fast-and-light trips.
From
£270.87
at Alpinetrek
11 photosSummer down#4Mountain Equipment
660 g of summer warmth with a +7 °C comfort rating, often discounted at Cotswold.
From
£199.95
at Cotswold Outdoor
Lightest premium#5PHD (Peak High Designs)
Made in Sheffield with 900 FP down: 670 g for a bag PHD rates to -5 °C.
From
£631
at PHD
7 photosCheapest down#6Decathlon Simond
A 700 g summer down bag with lab-tested ISO ratings for under £100.
From
£99.99
at Decathlon
5 photosThree-season all-rounder#7Marmot
740 g of 800+ FP goose down, ISO-tested comfort 2 °C / limit -3 °C, from about £359 in the UK.
From
£358.90
at Hardloop
11 photosBest value#8Alpkit
Hydrophobic 750 FP RDS down with a -4 °C comfort rating for under £300, direct from Alpkit.
From
£274.99
at Alpkit
Lightest for warmth#9Cumulus
Polish-made 850 FP goose-down bag that undercuts the big brands; ships from Poland.
From
£289
at Cumulus
11 photosBest all-rounder#10Mountain Equipment
The 3-season benchmark: 0 °C comfort at 820 g, widely stocked and often discounted.
From
£240
at Trekitt
Budget down#11Decathlon Simond
A no-frills three-season down bag that undercuts the outdoor brands by £100.
From
£149.99
at Decathlon
Premium pick#12Rab
Rab's hand-filled 800 FP classic, now named by temperature: 0 °C comfort at 870 g.
From
£401.76
at Alpinetrek
Value shoulder-season#13Decathlon Simond
0 °C ISO comfort under a kilo, for spring and autumn camps in the hills.
From
£169.99
at Decathlon
10 photosFirst down bag#14Mountain Equipment
Mountain Equipment's entry-level down bag: 940 g, comfort 1 °C, from £140 discounted.
From
£140
at Trekitt
2 photosThree-season plus#15Mountain Equipment
-1 °C comfort in a box-walled bag that bridges three-season and winter.
From
£320
at Adapt Outdoors
11 photosRoomy camp down#16Sea to Summit
A roomy 1119 g down bag with ISO comfort 3 °C that unzips flat into a quilt; around £211 discounted.
From
£210.67
at Alpinetrek
Weights and sizes are manufacturer figures. Prices were checked on 31 October 2026 and change daily, so confirm on the retailer's site.
A bag called "400" tells you the fill weight, not the warmth. The ISO 23537 comfort rating is the temperature a cold sleeper stays comfortable at. Treat the limit rating as a survival figure.
800 fill-power down lofts more per gram than 650, so the bag is lighter and packs smaller for the same warmth. Fill weight times fill power is a rough proxy for warmth.
Treated down resists the condensation of a tent or bivvy for a night or two. It is not waterproof. Keep the bag in a dry bag regardless.
Dead air space costs warmth. A narrow mummy cut is warmer for its weight; a relaxed cut is more pleasant for side sleepers. Check the shoulder girth.
Methodology
Specs are manufacturer figures, or a UK specialist retailer's spec sheet where the maker is vague. Prices were checked on 31 October 2026. Our ratings are editorial and explained on the how we test page.
