Sierra Designs
Sierra Designs Nitro 800 Down Sleeping Bag (-9 °C)
Where it fits
- Also works for
- Backpacking and wild camping
- Not for
- Winter mountain
Why these labels
- Backpacking and wild camping: Light to carry: 0.9 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: 6/10 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: 7/10 How much it adds to your pack, compared with the whole market.
Comfort -2 °C, limit -9 °C (EN 13537).
Three-season backpacking in the UK, including nights down to light frost
- Comfort
- -2 °C
- Limit
- -9 °C
- Fill
- 800 fill down
- Weight
- 880 g (Regular)
Packed size 10.8 L, 38 cm long and 19 cm across Compare with a 2-litre bottle
A bit longer than a 2-litre bottle and about twice as wide. Drawn to scale.
Where to buy
S2AS £320 In stock. Free delivery. Regular. Free UK delivery over £100.
View at shop: S2ASUltralight Outdoor Gear £224.99 Out of stock. Regular out of stock on 2 Nov 2026 (the Long is in stock at £234.99). Shop RRP £319.99.
View at shop: Ultralight Outdoor GearPrices checked 2 Nov 2026 to 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.
Sierra Designs' EN comfort -2 °C (limit -9 °C) sits in the -4.9 to 0 °C band: good for spring and autumn with light frost, not a winter bag.
Room inside
Estimate: only 2 reviews about room inside (fewer than the 3 we need, so never above 8) 8/10How much room to move, bend your knees and sleep on your side. Roomier is comfier. 8: Clearly better than most.
Two reviewers say it is roomy for a mummy bag, with space to sleep on your side and spread your knees.
Weight
From maker's figures 7/10How much it adds to your pack. 7: Better than most.
880 g (Regular, Sierra Designs' published minimum weight) sits in the 700–999 g band; one shop lists 842 g without the storage bags.
Packed size
From maker's figures 4/10How much room it takes in your rucksack. 4: A bit below average.
Sierra Designs gives a stuff sack of 38 x 19 cm (length x width), so 3.1416 x 9.5 x 9.5 x 38 = 10,775 cm³, so 10.8 L, in the 9–12.9 L band; a compression sack would pack it smaller.
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 8/10How comfy the shape, hood and fabric feel; not the temperature rating.
4 reviews on comfort to sleep in, e.g. "I actually really like the feeling of this bag".
Zip*
Estimate: only 2 reviews about zip (fewer than the 3 we need, so never above 8) 7/10How smoothly the zip runs without snagging.
2 reviews on zip, e.g. "not entirely snag-proof, but more importantly, it’s very easy to free it if and when it does snag on the inside fabric".
In short
Good for
- Three-season backpacking in the UK, including nights down to light frost
- Hot-footed sleepers who like a foot vent in a mummy bag
Strengths
- Comfort rating of -2 °C (limit -9 °C) for under 900 g
- Self-sealing foot vent lets you cool your feet without kicking the covers off
- 800-fill hydrophobic down that is PFC-free
- Draught collar and 13 cm baffles with side-wall baffles to stop the down shifting
Weaknesses
- Packs to about 10.8 L in its stuff sack, bigger than ultralight bags of similar warmth
- A roomy cut for a mummy bag means more air to heat for smaller or colder sleepers
- Regular fits people up to 183 cm; a Long is sold for taller sleepers
- Only one independent review found, so damp, comfort and durability are 'Not enough evidence'
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.
ShowHide sources (6)
- S2AS: Sierra Designs Nitro 800F 20 Deg sleeping bag page (copy of Sierra Designs' EN rating, weight and size specification; Sierra Designs no longer lists this bag)
- Wild Camp Phil (YouTube): Best 3 Season Sleeping Bag? Sierra Designs Nitro 20
- The Big Outside: Sierra Designs Nitro 800 20-degree sleeping bag review
- Andrew Skurka: Sierra Designs Nitro 800 0/20/35 degree mummy bag review
- Backcountry Exposure (YouTube): What’s The Better Bag? Thermarest Hyperion vs Sierra Designs Nitro
- CleverHiker: Sierra Designs Nitro UL 20 Sleeping Bag Review