Sea to Summit
Spark SpII Ultralight Down Sleeping Bag
$409
Best Sleeping Bags · head-to-head
Spark SpII Ultralight Down Sleeping Bag vs Sidewinder SL 20 Mummy Sleeping Bag
A sourced, side-by-side comparison. Sidewinder SL 20 Mummy Sleeping Bag is cheaper at $199.96. Every spec and price links to its source.
Big Agnes
Sidewinder SL 20 Mummy Sleeping Bag
$199.96Cheaper
Which is better: the Spark SpII Ultralight Down Sleeping Bag or Sidewinder SL 20 Mummy Sleeping Bag?
The Spark SpII Ultralight Down Sleeping Bag wins 1 of the 1 specs we compare head to head; the other wins 0. The Sidewinder SL 20 Mummy Sleeping Bag is the cheaper at $199.96. Get the Spark SpII Ultralight Down Sleeping Bag for the stronger spec sheet, the Sidewinder SL 20 Mummy Sleeping Bag to spend less.
See Spark SpII Ultralight Down Sleeping Bag on Amazon See 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 | Spark SpII Ultralight Down Sleeping Bag | 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 — Spark SpII Ultralight Down Sleeping Bag: advnture.com (verified 2026-06-20). Sidewinder SL 20 Mummy Sleeping Bag: bigagnes.com (verified 2026-06-20).
What's the difference between the Spark SpII Ultralight Down Sleeping Bag and 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: Spark SpII Ultralight Down Sleeping Bag 28 vs Sidewinder SL 20 Mummy Sleeping Bag 20
- Fill power: Spark SpII Ultralight Down Sleeping Bag 850 vs Sidewinder SL 20 Mummy Sleeping Bag 650
- Packed weight (lb): Spark SpII Ultralight Down Sleeping Bag 1.17 vs Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: Spark SpII Ultralight Down Sleeping Bag 2.5 L (approx. 1-liter bottle size) vs Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Product note: 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 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