Western Mountaineering
Western Mountaineering UltraLite Sleeping Bag
$660
Best Sleeping Bags · head-to-head
Western Mountaineering UltraLite 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 Western Mountaineering UltraLite Sleeping Bag or Big Agnes Sidewinder SL 20 Mummy Sleeping Bag?
The Western Mountaineering UltraLite 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 Western Mountaineering UltraLite Sleeping Bag for the stronger spec sheet, the Big Agnes Sidewinder SL 20 Mummy Sleeping Bag to spend less.
See Western Mountaineering UltraLite 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 | Western Mountaineering UltraLite Sleeping Bag | Big Agnes Sidewinder SL 20 Mummy Sleeping Bag |
|---|---|---|
| US price | $660 | $199.96 |
| Brand | Western Mountaineering | Big Agnes |
| Released | — | — |
| 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 |
Sources — Western Mountaineering UltraLite Sleeping Bag: westernmountaineering.com (verified 2026-09-21). Big Agnes Sidewinder SL 20 Mummy Sleeping Bag: campman.com (verified 2026-06-20).
What's the difference between the Western Mountaineering UltraLite 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.
- Fill power: Western Mountaineering UltraLite Sleeping Bag 850 vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 650
- Packed weight (lb): Western Mountaineering UltraLite Sleeping Bag 1.81 vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: Western Mountaineering UltraLite Sleeping Bag 7 x 13 in vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Zipper side: Western Mountaineering UltraLite Sleeping Bag left or right vs Big Agnes Sidewinder SL 20 Mummy Sleeping Bag center
- Product note: Western Mountaineering 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 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