Kelty
Cosmic Down 20 Sleeping Bag
$189.95Cheaper
Released 2024
Best Sleeping Bags · head-to-head
Cosmic Down 20 Sleeping Bag vs Sidewinder SL 20 Mummy Sleeping Bag
A sourced, side-by-side comparison. Cosmic Down 20 Sleeping Bag is cheaper at $189.95. Every spec and price links to its source.
Big Agnes
Sidewinder SL 20 Mummy Sleeping Bag
$199.96
Which is better: the Cosmic Down 20 Sleeping Bag or Sidewinder SL 20 Mummy Sleeping Bag?
The Sidewinder SL 20 Mummy Sleeping Bag wins 1 of the 1 specs we compare head to head; the other wins 0. The Cosmic Down 20 Sleeping Bag is the cheaper at $189.95. Get the Sidewinder SL 20 Mummy Sleeping Bag for the stronger spec sheet, the Cosmic Down 20 Sleeping Bag to spend less.
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Full spec sheet
✓ marks the stronger figure where "more" — or "less", for price and weight — is unambiguously better.
| Spec | Cosmic Down 20 Sleeping Bag | Sidewinder SL 20 Mummy Sleeping Bag |
|---|---|---|
| US price | $189.95 MSRP, regular size, per kelty.com | $199.96 |
| Brand | Kelty | Big Agnes |
| Released | 2024 | — |
| Temperature rating f | 20 | 20 |
| Insulation type | down | down |
| Fill power | 550 | 650 |
| Shape | semi-rectangular | mummy |
| Packed weight (lb) | 2.44 | 2.25 |
| Packed size | 8 x 13 in | 6.5 x 8 in |
| Zipper side | right | center |
| Product note | 550-fill DriDown; ISO comfort 31F, lower limit 21F; regular weight 2 lb 7 oz | 650-fill DownTek hydrophobic down with body-mapped FireLine ECO synthetic at pressure points; designed for side sleepers; center ambidextrous zipper |
Sources — Cosmic Down 20 Sleeping Bag: kelty.com (verified 2026-06-20). Sidewinder SL 20 Mummy Sleeping Bag: bigagnes.com (verified 2026-06-20).
What's the difference between the Cosmic Down 20 Sleeping Bag and Sidewinder SL 20 Mummy Sleeping Bag?
Where the two actually differ on the specs we track (6 of 8). Matching specs are omitted.
- Fill power: Cosmic Down 20 Sleeping Bag 550 vs Sidewinder SL 20 Mummy Sleeping Bag 650
- Shape: Cosmic Down 20 Sleeping Bag semi-rectangular vs Sidewinder SL 20 Mummy Sleeping Bag mummy
- Packed weight (lb): Cosmic Down 20 Sleeping Bag 2.44 vs Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: Cosmic Down 20 Sleeping Bag 8 x 13 in vs Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Zipper side: Cosmic Down 20 Sleeping Bag right vs Sidewinder SL 20 Mummy Sleeping Bag center
- Product note: Cosmic Down 20 Sleeping Bag 550-fill DriDown; ISO comfort 31F, lower limit 21F; regular weight 2 lb 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
What reviewers say
Sourced tester consensus for each — the "what people who used it think" layer, not just specs.
Cosmic Down 20 Sleeping Bag
Two whitelisted hands-on testers (CleverHiker, Switchback Travel) reviewed the Kelty Cosmic Down 20 and both call it a strong-value budget 3-season down bag. Both praise its warmth-to-weight ratio, buttery-soft lining, and low price, and both flag it as heavy and bulky for a backpacking-specific bag while noting the large gap between the women's and unisex versions. CleverHiker's tester observed comfortable warmth to 30F against the 20F spec. All six quotes and the one measured value were verified as literal substrings of the fetched source text. (2 sourced reviews, 2 lab-tested.)
Praised: Excellent warmth-to-weight ratio and cozy, buttery-soft lining; Strong value / affordable for a down bag; Draft collar/tubes and adjustable hood seal in heat well for 3-season use.
Flagged: Heavy and bulky for a backpacking-specific down bag; Large price and weight gap between women's and unisex versions; Narrow mummy fit limits room to spread out.
Sidewinder SL 20 Mummy Sleeping Bag
No sourced tester review yet.