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Sea to Summit Spark SP II Sleeping Bag — Specs & Analysis
Manufacturer specifications, compared against every other sleep systems in our database. We do not test gear in the field — we measure, verify, and compare.
The Spark SP II is a traditional mummy bag that packs down to the size of a water bottle. The 850+ fill Ultra-Dry Down resists moisture, and the differential cut reduces cold spots. One of the most compressible bags available.
Who Is the Sea to Summit Spark SP II Sleeping Bag Best For?
Bikepackers who prioritize packed size above all else. If that describes your riding style, the Spark SP II Sleeping Bag should be at the top of your shortlist. It sits in the Sleep Systems category alongside 19 other products we track.
How It Compares
At 520g and $299, the Spark SP II Sleeping Bag is 270g heavier than the lightest option in this category (the Therm-a-Rest NeoAir UberLite at 250g). The most budget-friendly option is the Cascade Designs Therm-a-Rest Z Lite Sol at $50.
The price-to-weight ratio comes in at $58 per 100g — a premium price point, but you're paying for quality, materials, and design that justify the investment for serious bikepackers.
What We Like
- +Incredibly compressible — water bottle size
- +850+ Ultra-Dry Down
- +Well-designed hood and draft collar
- +Excellent for side sleepers
Watch Out For
- −28F limit is optimistic in practice
- −Narrow cut won't suit all body types
- −Pricey for a 28F bag
The Bottom Line
We haven't scored the Sea to Summit Spark SP II Sleeping Bag, and neither has anyone else we can cite. It's here for its verified specifications and dimensions, which is what the fit tools run on — a score is an editorial judgement, and we don't hand one out until someone has a basis for it. What this page can tell you is measured: 520g, $299, and how both sit against every other sleep systems product we track.
The price and weight above have not yet been checked against the manufacturer's own page. We are working through the catalogue and saying so as we go, rather than letting silence imply otherwise.
Specifications and dimensions come from the sources listed above. Where a page draws on first-hand riding, it says so.
What it packs down to
Sea to Summit publishes a packed size of 5.5" x 8.5", which is 3.3 litres as a stuff sack. Of the 55 bags we track that publish a capacity, 38 have room for it and 17 do not.
Volume is computed from Sea to Summit's own packed size, treating a two-dimension figure as a stuff sack. Bag capacities are the makers' published figures, not ours — 12 of the bags we hold dimensions for publish no capacity and are left out of the count rather than assumed. A stuff sack does not reshape itself, so read the headroom as room to spare rather than a guarantee it goes in easily.
How it compares
Against the 20 sleep systems we hold published specs for.
At 520g the Spark SP II Sleeping Bag is lighter than 5 of 19 alternatives we track. The category median is 465g.
At $299 it undercuts 5 of 19 of them, against a median of $235. That works out at $58 per 100g — above the $51 median for sleep systems.
Weight and price come from published specifications. Cost per 100g is a blunt measure — it rewards light gear and says nothing about durability or whether the thing works — so treat it as one input, not a verdict.
More in Sleep Systems
Sleeping bags, quilts, and pads that pack small and keep you warm on the trail.