Mountain Equipment
Mountain Equipment Helium GT 400 (Regular)
Best use
- Made for
- Bikepacking, Backpacking and wild camping
- Not for
- Winter mountain
Why these labels
- Bikepacking: The maker states this use, and the published specs do not rule it out.
- Backpacking and wild camping: The maker states this use, and the published specs do not rule it out.
- Winter mountain: Comfort rating 0 °C: too cold for winter nights
From the maker's stated use and the published specs.
- Summer wild camp: 5/10 UK, roughly May to September, nights above about 8 °C, sheltered pitches.
- Three-season hills: 6/10 UK hills in spring and autumn. Wind, rain, and nights near freezing.
- 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: 7/10 How much it adds to your pack, compared with the whole market.
Comfort 0 °C, limit -6 °C (ISO 23537).
Side sleepers and larger people who want an ultralight down bag with more room
- Zip side
- Left
- Comfort
- 0 °C
- Limit
- -6 °C
- Fill
- 700 fill down
- Weight
- 890 g (Regular)
Packed size 10.1 L, 24 x 21 x 20 cm Compare with a 2-litre bottle
Shorter than a 2-litre bottle and about twice as wide. Drawn to scale.
Where to buy
Ultralight Outdoor Gear £279.99 In stock. Free delivery. Regular size, 2 in stock when checked.
View at shop: Ultralight Outdoor GearMountain Equipment £330 Out of stock. Shows 'Coming soon'.
View at shop: Mountain EquipmentPrices 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 7/10How cold a night you can sleep comfortably through. 7: Better than most.
Maker's comfort figure of 0 °C (limit -6 °C, extreme -24 °C) sits in the -4.9 to 0 °C band. The maker names EN 13537/ISO 23537 but not the edition; its own 'Good Night's Sleep' figure of -5 °C is not used.
Room inside
Estimate from maker's specs: bag shape (fewer than 3 reviews about room) 3/10How much room to move, bend your knees and sleep on your side. Roomier is comfier. 3: Below average. Fine for some trips, not others.
No review we found says how roomy it is, so this is an estimate from the bag shape.
Weight
From maker's figures 7/10How much it adds to your pack. 7: Better than most.
The maker's 890 g for the Regular sits in the 700–999 g band (one shop lists 894 g, same band).
Packed size
From maker's figures 4/10How much room it takes in your rucksack. 4: A bit below average.
Maker's packed size 24 x 21 x 20 cm: 24 x 21 x 20 = 10,080 cm³, so 10.1 L, in the 9–12.9 L band.
In short
Good for
- Side sleepers and larger people who want an ultralight down bag with more room
- Spring and early-summer UK camps and cycle-touring where nights stay above freezing
- Anyone who finds the standard Helium's 78 cm inside width too tight
Strengths
- 890 g with a comfort rating of 0 °C and a limit of -6 °C
- Wider cut than the standard Helium: 82 cm inside width and 60 cm foot width, against 78 cm and 52 cm, per the maker's size guides
- 449 g of 700+ fill duck down
- Full-length Gemini zip baffle (140 cm zip), draught collar and five-baffle hood, per the maker
Weaknesses
- Packs to about 10 L, larger than most down bags in this weight band
- The down is not water-resistant treated, so a wet bag loses warmth
- Only 0 °C comfort: not a bag for freezing nights
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.