Marmot
Marmot Hydrogen Down Sleeping Bag (-3 °C)
Where it fits
- Also works for
- Bikepacking, Backpacking and wild camping
- Not for
- Winter mountain
Why these labels
- Bikepacking: Small enough for bike bags: packs to 5.5 litres
- Backpacking and wild camping: Light to carry: 0.7 kg
- Winter mountain: Comfort rating 2 °C: too cold for winter nights
From the maker's stated use and the published specs.
- Summer wild camp: 7/10 UK, roughly May to September, nights above about 8 °C, sheltered pitches.
- Three-season hills: 4/10 UK hills in spring and autumn. Wind, rain, and nights near freezing. Capped at 4: needs warmth 7+ (comfort 0 °C or colder).
- Winter camp: 4/10 UK winter or high ground. Below freezing, strong wind, possibly snow. Capped at 4: needs warmth 9+ (comfort -5 °C or colder).
- Weight: 8/10 How much it adds to your pack, compared with the whole market.
Comfort 2 °C, limit -3 °C (ISO 23537).
Three-season backpacking in the UK where weight and pack size matter, on nights down to about freezing
- Zip side
- Left
- Comfort
- 2 °C
- Limit
- -3 °C
- Fill
- 800 fill down
- Weight
- 740 g (Regular)
Packed size 5.5 L, 31 cm long and 15 cm across Compare with a 2-litre bottle
About as long as a 2-litre bottle and about one and a half times as wide. Drawn to scale.
Where to buy
Alpinetrek £368.96 In stock. Free delivery. Regular, left zip.
View at shop: AlpinetrekUltralight Outdoor Gear £399.99 In stock. Free delivery. Regular. Shop RRP £439.99.
View at shop: Ultralight Outdoor GearPrices checked 8 Nov 2026 on each shop's own page; shops can change them. We earn no commission on these links; shops are listed by price. More
Our ratings (out of 10)
1 to 10, compared with the whole market. Each says what it's based on. How we score
Warmth
From maker's figures 6/10How cold a night you can sleep comfortably through. 6: A bit better than average.
Marmot's ISO comfort 2 °C (limit -3 °C) sits in the 0.1 to 5 °C band: a spring-to-autumn bag for cool nights, with cold sleepers needing more for frost.
Room inside
From reviews 7/10How much room to move, bend your knees and sleep on your side. Roomier is comfier. 7: Better than most.
Roomy through the shoulders for an ultralight mummy, which testers liked. OutdoorGearLab found the foot box tight.
Weight
From maker's figures 8/10How much it adds to your pack. 8: Clearly better than most.
740 g (Regular, Marmot's figure) sits in the 700–999 g band.
Packed size
From maker's figures 7/10How much room it takes in your rucksack. 7: Better than most.
Marmot gives a pack size of 31 x 15 cm (length x width), so 3.1416 x 7.5 x 7.5 x 31 = 5,478 cm³, so 5.5 L, in the 4–5.9 L band.
What reviewers say (out of 10)
Ratings marked * are from reviews and are not part of the trip score. They are reviewers' scores, not our own measurements. How we score
Comfort to sleep in*
Estimate: only 2 reviews about comfort to sleep in (fewer than the 3 we need, so never above 8) 7/10How comfy the shape, hood and fabric feel; not the temperature rating.
2 reviews on comfort to sleep in, e.g. "We also heard complaints about the drawcord used to seal up the hood.".
Zip*
Estimate: only 2 reviews about zip (fewer than the 3 we need, so never above 8) 6/10How smoothly the zip runs without snagging.
2 reviews on zip, e.g. "we're not fans of the tiny zipper it relies on because it's so prone to snagging.".
Reviewers disagree on this.
In short
Good for
- Three-season backpacking in the UK where weight and pack size matter, on nights down to about freezing
- Anyone who likes a second fold-down zip for venting or for sitting up in the bag
Strengths
- 740 g and 5.5 L for a 2 °C comfort rating (limit -3 °C)
- 800+ fill goose down with a water-repellent ExpeDry treatment, RDS certified
- Main zip plus a short fold-down second zip for ventilation and easy entry
- Recycled shell and lining fabrics
- One long-term reviewer found it roomier than other ultralight three-season bags, with plenty of room for the feet
Weaknesses
- Comfort rating of 2 °C is only just below spring-night temperatures, so it's a three-season bag rather than a frost bag
- Earlier Hydrogens were criticised for a narrow footbox; the one independent review of this version found plenty of foot room
- Only one independent review of this version found, so comfort, damp and durability are 'Not enough evidence'
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.