Western Mountaineering
UltraLite Sleeping Bag
$660
Best Sleeping Bags · head-to-head
UltraLite 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 UltraLite Sleeping Bag or Sidewinder SL 20 Mummy Sleeping Bag?
The UltraLite 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 UltraLite Sleeping Bag for the stronger spec sheet, the Sidewinder SL 20 Mummy 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 | UltraLite Sleeping Bag | 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 — UltraLite Sleeping Bag: westernmountaineering.com (verified 2026-06-20). Sidewinder SL 20 Mummy Sleeping Bag: bigagnes.com (verified 2026-06-20).
What's the difference between the UltraLite 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.
- 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