Sea to Summit Spark Ultralight Down Sleeping Bag
Best for
Best ultralight
Amazon rating
Amazon aggregate, one input among many in the Verdict Score
Based on 2 trusted sources
Current price
$261.75
Updated May 18, 2026 · 1 min read
Sources behind this verdict
10 reviewers weighted by source trust
The consensus
What reviewers found
Synthesized across the trust-weighted source mix below.
Across the reviewers we read, the Sea to Summit Spark is the clear pick when packed size and weight matter most. CleverHiker highlights the 850+ fill-power goose down and lofty baffle construction, and OutdoorGearLab specifically notes that unlike most ultralight bags they've tested, the Spark is comfortably proportioned rather than coffin-like. Backwoods Pursuit and Bikepacking.com reinforce the warmth-to-weight verdict, with the latter calling out a generously sized footbox.
What reviewers liked
- CleverHiker and OutdoorGearLab both endorse the 850+ fill power warmth-to-weight ratio
- OutdoorGearLab praises the unusually roomy cut for an ultralight bag
- Bikepacking.com calls out a generous footbox that other ultralight bags lack
- Water-resistant down and shell help in damp shoulder-season conditions per Backwoods Pursuit
Where it falls short
- r/Ultralight users consistently pan the half-zip as nearly impossible to vent
- Premium pricing, well above the budget and mid-tier picks in this category
- r/bikepacking flags that down can lose loft on extended wet trips
- Older versions had zipper QC issues per community reports
Across the reviewers we read, the Sea to Summit Spark is the clear pick when packed size and weight matter most. CleverHiker highlights the 850+ fill-power goose down and lofty baffle construction, and OutdoorGearLab specifically notes that unlike most ultralight bags they've tested, the Spark is comfortably proportioned rather than coffin-like. Backwoods Pursuit and Bikepacking.com reinforce the warmth-to-weight verdict, with the latter calling out a generously sized footbox.
The near-universal complaint is the half-length zipper. Multiple r/Ultralight threads call it 'complete garbage' for venting, and one user on r/camping recommended a Western Mountaineering bag instead at a similar price point. r/bikepacking commenters also raise the standard down caveat: moisture management on multi-day wet trips is a real concern, and the Spark is not the bag for sustained rain.
For weight-conscious backpackers willing to pay a premium for an 850+ fill bag with a roomy cut, the consensus is that the Spark delivers; just go in knowing the zipper is a known weak point.
- nylon/polyester
- 45-degree Fahrenheit (7-degree Celsius) ultralight down sleeping bag for warm weather backpacking, bike packing, and touring
- High-loft 850+ fill power down insulation (Responsible Down Standard certified) with a non-PFC Ultra-Dry down treatment to improve reaction to moisture, retaining loft and performance
- Ultralight 10D shell with PFC-free DWR keeps the hood and footbox highly water resistant; breathable 10D nylon liner provides all-night comfort
- Contoured mummy shape provides adequate room for a natural sleeping position; YKK #5 zippers provide reliable, snag-free operation
- Baffle construction is sewn through for lighter weight; Sea to Summit Guarantee is offered for the Lifetime of this product
The half zipper absolutely sucks, so you can't vent it hardly at all. It packs down super small, and is fairly warm for its rating. If it had a ...
I have the western mountaineering ultra light 20 deg. It's so good. I can't recommend it enough. Pricey and worth it!
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“Sea To Summit Spark Sleeping Bag: 30F Down” · GH Review
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