Therm-a-Rest
Therm-a-Rest Hyperion -6 °C Down Sleeping Bag (Regular)
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 3.5 litres
- Backpacking and wild camping: Light to carry: 0.6 kg
- Winter mountain: Comfort rating 0 °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: 7/10 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: 9/10 How much it adds to your pack, compared with the whole market.
Comfort 0 °C, limit -6 °C (EN 13537).
Weight-first backpackers and fastpackers who sleep on their back
- Zip side
- Left
- Comfort
- 0 °C
- Limit
- -6 °C
- Fill
- 900 fill down
- Weight
- 580 g (Regular)
Packed size 3.5 L, 20 cm long and 15 cm across Compare with a 2-litre bottle
Shorter than a 2-litre bottle and about one and a half times as wide. Drawn to scale.
Where to buy
Ultralight Outdoor Gear £394.99 In stock. Free delivery.
View at shop: Ultralight Outdoor GearAbsolute Snow £469.95 Out of stock. Shop page says currently unavailable.
View at shop: Absolute SnowWildbounds £344.95 Out of stock.
View at shop: WildboundsPrices 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.
Therm-a-Rest's EN comfort figure of 0 °C sits in the -4.9 to 0 °C band; the limit is -6 °C. One cold-sleeping tester at Advnture was only comfortable down to about 3 °C.
Room inside
From reviews 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.
Four reviews agree the cut is narrow and snug, with little room to turn over. Two say it is especially restrictive for side sleepers.
Weight
From maker's figures 9/10How much it adds to your pack. 9: Among the best you can buy for this.
Therm-a-Rest's weight of 580 g (without sacks) sits in the under 700 g band.
Packed size
From maker's figures 9/10How much room it takes in your rucksack. 9: Among the best you can buy for this.
Therm-a-Rest gives a packed size of 15 x 20 cm but no volume. Reading it as 20 cm long and 15 cm across, it works out at about 3.5 L (3.1416 x 7.5 x 7.5 x 20 = 3,534 cm³), in the under 4 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*
Reviewers' average 7/10How comfy the shape, hood and fabric feel; not the temperature rating.
7 reviews on comfort to sleep in, e.g. "cozy and warm yet too restrictive in the lower half of the design".
Zip*
Reviewers' average 5/10How smoothly the zip runs without snagging.
5 reviews on zip, e.g. "I noticed that the zips were quite fiddly, however, and kept catching on the outer material".
In short
Good for
- Weight-first backpackers and fastpackers who sleep on their back
- Three-season hill and summer alpine camps where every gram counts
- Anyone who wants a full hooded bag that weighs about the same as a quilt
Strengths
- Only 580 g and about 3.5 L packed, among the lightest and smallest bags rated to 0 °C comfort
- 900-fill hydrophobic goose down, with 70% of the fill on top and sides where it is not squashed
- Box-baffle walls and a draft collar cut cold spots
- Hood and draft tube make it a full bag rather than a quilt, with straps to hold it on a mat
Weaknesses
- Very slim cut: 126 cm round the hip and 109 cm at the feet, and testers found it tight for side sleepers
- Half-length zip, so it is harder to get in and out of and to vent
- 10D shell and small zip: reviewers report a fiddly, snag-prone zip and a thin outer fabric that needs care
- A cold sleeper at Advnture was comfortable only to about 3 °C, so treat 0 °C as a best case
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.
ShowHide sources (8)
- Therm-a-Rest: Hyperion -6 °C Sleeping Bag specifications (EU site)
- Advnture: Therm-a-Rest Hyperion -6 °C Sleeping Bag review
- CleverHiker: Therm-a-Rest Hyperion Sleeping Bag review
- Bike Hike Safari: Therm-a-Rest Hyperion Sleeping Bag review
- Greenbelly: Therm-a-Rest Hyperion 20F review
- OutdoorGearLab: Therm-a-Rest Hyperion 20 review
- The Equipment Guide UK: Therm-a-rest Hyperion 20
- Trek Scotland review: Therm-a-Rest Hyperion 20F (three seasons in the Scottish Highlands, hosted by Ultralight Outdoor Gear)