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

A sourced, side-by-side comparison of the UltraLite Sleeping Bag (Western Mountaineering) and Sidewinder SL 20 Mummy Sleeping Bag (Big Agnes) among sleeping bags. Sidewinder SL 20 Mummy Sleeping Bag is the cheaper of the two at $199.96.

## Side by side

| Spec | UltraLite Sleeping Bag | Sidewinder SL 20 Mummy Sleeping Bag |
| --- | --- | --- |
| US price | $660 | $199.96 |
| Brand | Western Mountaineering | Big Agnes |
| Temperature rating f | 20 | 20 |
| Insulation type | down | down |
| Fill power | 850 | 650 |
| Shape | mummy | mummy |
| Packed weight (lb) | 1.81 | 2.25 |
| Packed size | 7 x 13 in | 6.5 x 8 in |
| Zipper side | left or right | center |
| Product note | 850+ FP ethically-sourced premium goose down; USA made; full-length #5 YKK zipper; 6'0" version weighs 1 lb 13 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: UltraLite Sleeping Bag 850 vs Sidewinder SL 20 Mummy Sleeping Bag 650
- Packed weight (lb): UltraLite Sleeping Bag 1.81 vs Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: UltraLite Sleeping Bag 7 x 13 in vs Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Zipper side: UltraLite Sleeping Bag left or right vs Sidewinder SL 20 Mummy Sleeping Bag center
- Product note: UltraLite Sleeping Bag 850+ FP ethically-sourced premium goose down; USA made; full-length #5 YKK zipper; 6'0" version weighs 1 lb 13 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

## Sources

- UltraLite Sleeping Bag: https://www.westernmountaineering.com/product/ultralite/ (westernmountaineering.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/western-mountaineering-ultralite-vs-big-agnes-sidewinder-sl-20/
Cite: Per The Front Desk Review, UltraLite Sleeping Bag ($660) vs Sidewinder SL 20 Mummy Sleeping Bag ($199.96) — sourced spec-by-spec comparison at https://frontdeskreview.com/gear/sleeping-bags/western-mountaineering-ultralite-vs-big-agnes-sidewinder-sl-20/
License: CC BY 4.0.