Big Agnes
Big Agnes Fly Creek UL Down Sleeping Bag (-4 °C)
Best use
- Made for
- Backpacking and wild camping
- Not for
- Winter mountain
Why these labels
- Backpacking and wild camping: The maker states this use, and the published specs do not rule it out.
- 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: 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 -4 °C (ISO 23537).
Spring-to-autumn hill and wild camps in the UK, including nights close to freezing
- Zip
- Half
- Comfort
- 2 °C
- Limit
- -4 °C
- Fill
- 850 fill down
- Weight
- 722 g (Regular)
Packed size 7.5 L, 24 cm long and 20 cm across Compare with a 2-litre bottle
Shorter than a 2-litre bottle and about twice as wide. Drawn to scale.
Where to buy
Alpinetrek £337.46 In stock. Free delivery. Regular, cheapest colour shown. Shop list price £449.95.
View at shop: AlpinetrekUltralight Outdoor Gear £404.99 In stock. Free delivery. Regular. Shop RRP £449.99.
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.
Big Agnes's ISO comfort 2 °C (limit -4 °C) sits in the 0.1 to 5 °C band: a three-season bag for spring and autumn, with cold sleepers needing a warmer one for frost.
Room inside
From reviews 5/10How much room to move, bend your knees and sleep on your side. Roomier is comfier. 5: Does the job. Average for wild-camping gear.
Reviewers agree it is a slim, tapered ultralight mummy: fine for slim builds, but restrictive for broader shoulders or hips and not the bag for wriggle room.
Weight
From maker's figures 8/10How much it adds to your pack. 8: Clearly better than most.
722 g (Regular, Big Agnes's figure) sits in the 700–999 g band, just over the 5-score line.
Packed size
From maker's figures 5/10How much room it takes in your rucksack. 5: Does the job. Average for wild-camping gear.
Big Agnes's compressed bag size is 24 cm long by 20 cm across, so it's a stuff sack: 3.1416 x 10 x 10 x 24 = 7,540 cm³, so 7.5 L, in the 6–8.9 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*
Reviewers' average 7/10How comfy the shape, hood and fabric feel; not the temperature rating.
4 reviews on comfort, e.g. "allowing full upper body movement while still staying partly in your bag".
Zip*
Estimate: only 2 reviews about the zip (fewer than the 3 we need, so never above 8) 6/10How smoothly the zip runs without snagging.
2 reviews on the zip, e.g. "It has a regular-style small zip which runs pretty snag free.".
Reviewers disagree on this.
In short
Good for
- Spring-to-autumn hill and wild camps in the UK, including nights close to freezing
- Backpackers who put weight and pack space first and are happy to handle a delicate shell with care
Strengths
- 722 g for a 2 °C comfort rating (limit -4 °C) and 850-fill down
- Packs to about 7.5 L, smaller with a compression sack
- Down is treated to repel water, and one reviewer found it coped with damp UK November air
- Centre half zip lets you sit up in the bag at camp
- Shell is made from recycled fishing nets and the down is RDS certified
Weaknesses
- Tapered mummy fit is snug on broad shoulders or hips, and the footbox is narrow
- Half-length zip can snag and gives little venting on warm nights
- The thin 10D shell needs gentle handling and absorbs spilt water if left wet
- Comfort rating of 2 °C means cold sleepers will want something warmer for frost
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.
ShowHide sources (6)
- Big Agnes: Fly Creek UL 25° product page (ISO comfort and limit, fill, compressed size)
- The Great Outdoors: Big Agnes Fly Creek UL25 review
- Live for the Outdoors: Big Agnes Fly Creek UL25 sleeping bag review
- T3: Big Agnes Fly Creek UL 25° review
- Biketour Global: Fly Creek UL sleeping bag in bikepacking test
- Wilderness (NZ): Big Agnes Fly Creek UL 25 Sleeping Bag review (ratings read; text is behind a paywall)