Sea to Summit
Sea to Summit Spark SpII Ultralight Down Sleeping Bag
$409
Best Sleeping Bags · head-to-head
Sea to Summit Spark SpII Ultralight Down Sleeping Bag vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag
A sourced, side-by-side comparison. Big Agnes Sidewinder SL 20 Mummy Sleeping Bag is cheaper at $199.96. Every spec and price links to its source.
Big Agnes
Big Agnes Sidewinder SL 20 Mummy Sleeping Bag
$199.96Cheaper
Which is better: the Sea to Summit Spark SpII Ultralight Down Sleeping Bag or Big Agnes Sidewinder SL 20 Mummy Sleeping Bag?
The Sea to Summit Spark SpII Ultralight Down Sleeping Bag wins 1 of the 1 specs we compare head to head; the other wins 0. The Big Agnes Sidewinder SL 20 Mummy Sleeping Bag is the cheaper at $199.96. Get the Sea to Summit Spark SpII Ultralight Down Sleeping Bag for the stronger spec sheet, the Big Agnes Sidewinder SL 20 Mummy Sleeping Bag to spend less.
See Sea to Summit Spark SpII Ultralight Down Sleeping Bag on Amazon See Big Agnes Sidewinder SL 20 Mummy Sleeping Bag on Amazon
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Full spec sheet
✓ marks the stronger figure where "more" — or "less", for price and weight — is unambiguously better.
| Spec | Sea to Summit Spark SpII Ultralight Down Sleeping Bag | Big Agnes Sidewinder SL 20 Mummy Sleeping Bag |
|---|---|---|
| US price | $409 | $199.96 |
| Brand | Sea to Summit | Big Agnes |
| Released | — | — |
| Temperature rating f | 28 | 20 |
| Insulation type | down | down |
| Fill power | 850 | 650 |
| Shape | mummy | mummy |
| Packed weight (lb) | 1.17 | 2.25 |
| Packed size | 2.5 L (approx. 1-liter bottle size) | 6.5 x 8 in |
| Zipper side | — | center |
| Product note | Lower limit 28F / -2C; comfort 38F / 4C; Ultra-Dry Down PFAS-free treatment; regular size; 530 g / 18.7 oz | 650-fill DownTek hydrophobic down with body-mapped FireLine ECO synthetic at pressure points; designed for side sleepers; center ambidextrous zipper |
Sources — Sea to Summit Spark SpII Ultralight Down Sleeping Bag: advnture.com (verified 2026-06-20). Big Agnes Sidewinder SL 20 Mummy Sleeping Bag: campman.com (verified 2026-06-20).
What's the difference between the Sea to Summit Spark SpII Ultralight Down Sleeping Bag and Big Agnes Sidewinder SL 20 Mummy Sleeping Bag?
Where the two actually differ on the specs we track (5 of 8). Matching specs are omitted.
- Temperature rating f: Sea to Summit Spark SpII Ultralight Down Sleeping Bag 28 vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 20
- Fill power: Sea to Summit Spark SpII Ultralight Down Sleeping Bag 850 vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 650
- Packed weight (lb): Sea to Summit Spark SpII Ultralight Down Sleeping Bag 1.17 vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: Sea to Summit Spark SpII Ultralight Down Sleeping Bag 2.5 L (approx. 1-liter bottle size) vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Product note: Sea to Summit Spark SpII Ultralight Down Sleeping Bag Lower limit 28F / -2C; comfort 38F / 4C; Ultra-Dry Down PFAS-free treatment; regular size; 530 g / 18.7 oz vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 650-fill DownTek hydrophobic down with body-mapped FireLine ECO synthetic at pressure points; designed for side sleepers; center ambidextrous zipper