Sea to Summit
Sea to Summit Spark -9 °C Ultralight Down Sleeping Bag (Regular)
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: 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: 8/10 How much it adds to your pack, compared with the whole market.
Comfort -2 °C, limit -9 °C (ISO 23537).
Ultralight three-season and shoulder-season wild camps where weight and pack space matter most
- Comfort
- -2 °C
- Limit
- -9 °C
- Fill
- 850 fill down
- Weight
- 730 g (Regular)
- Packed
- 6.8 L
Where to buy
Snow+Rock £399.95 In stock. Free delivery.
View at shop: Snow+RockUltralight Outdoor Gear £424.99 In stock. Free delivery.
View at shop: Ultralight Outdoor GearSea to Summit £500 In stock. Free delivery. Free delivery over £75.
View at shop: Sea to SummitPrices 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.
Maker's ISO comfort rating is -2 °C (lower limit -9 °C), in the -4.9 to 0 °C band. The -9 in the name is the lower limit.
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 8/10How much it adds to your pack. 8: Clearly better than most.
730 g (Regular, maker's table) sits in the 700-999 g band. Ultralight Outdoor Gear lists 740 g.
Packed size
From maker's figures 6/10How much room it takes in your rucksack. 6: A bit better than average.
Maker's compressed volume is 6.8 L, in the 6-8.9 L band. The supplied compression sack is a 13 L size, which is not the compressed volume.
In short
Good for
- Ultralight three-season and shoulder-season wild camps where weight and pack space matter most
- Cold nights down to about 0 °C comfort (-2 °C ISO comfort) in a bag under 750 g
- Fast and light trips and bikepacking where a down bag needs to compress small
Strengths
- 730 g for a bag with a -2 °C ISO comfort rating and -9 °C lower limit
- Compresses to 6.8 L by the maker's figure
- 850+ fill goose down with Ultra-Dry Down water-repellent treatment, and a water-resistant hood and footbox against tent-wall condensation (maker's claim)
- Three-quarter-length zip with draught tube, plus a draught collar and box-wall baffles to limit cold spots
- Maker's ISO ratings come from a lab test
Weaknesses
- 10 denier shell is very thin, so it needs care around thorns, rough ground and sharp gear
- Snug mummy cut, so not a roomy bag
- No independent review of this exact bag found, so comfort, damp performance and durability are estimates, not reviewed scores
- The Spark Pro is the pricier sibling with 900+ fill down; the plain Spark is the cheaper choice
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.