# Cosmic Down 20 Sleeping Bag vs Sidewinder SL 20 Mummy Sleeping Bag: specs and price compared

A sourced, side-by-side comparison of the Cosmic Down 20 Sleeping Bag (Kelty) and Sidewinder SL 20 Mummy Sleeping Bag (Big Agnes) among sleeping bags. Cosmic Down 20 Sleeping Bag is the cheaper of the two at $189.95.

## Side by side

| Spec | Cosmic Down 20 Sleeping Bag | Sidewinder SL 20 Mummy Sleeping Bag |
| --- | --- | --- |
| US price | $189.95 | $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 |

## Key differences

- 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

**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.)

## Sources

- Cosmic Down 20 Sleeping Bag: https://kelty.com/products/cosmic-down-20 (kelty.com, verified 2026-06-20)
- Sidewinder SL 20 Mummy Sleeping Bag: https://www.bigagnes.com/products/sidewinder-sl-20 (bigagnes.com, verified 2026-06-20)

Canonical: https://frontdeskreview.com/gear/sleeping-bags/kelty-cosmic-down-20-vs-big-agnes-sidewinder-sl-20/
Cite: Per The Front Desk Review, Cosmic Down 20 Sleeping Bag ($189.95) vs Sidewinder SL 20 Mummy Sleeping Bag ($199.96) — sourced spec-by-spec comparison at https://frontdeskreview.com/gear/sleeping-bags/kelty-cosmic-down-20-vs-big-agnes-sidewinder-sl-20/
License: CC BY 4.0.