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#10 on this list
Ultima Thule -20
Wiggy's
Lamilite continuous-filament synthetic. Bulky, indestructible, and it still insulates soaked — a bush-Alaska staple.
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#1 on this list
Puma GWS -25°F
Western Mountaineering
The American benchmark. 850+ fill, continuous baffles, and a collar that seals like a gasket.
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Specs side by side
| Spec | Ultima Thule -20 | Puma GWS -25°F |
|---|---|---|
| Insulation Type | Lamilite Continuous-Filament Synthetic | Premium Down |
| Temperature Rating | -20°F | -25°F (-32°C) |
| Shell Material | Nylon | Gore Windstopper Fabric |
| Zipper | Full-length, heavy-duty | — |
| Manufactured | USA | — |
| Fill Power | — | 850+ Fill Goose Down |
| Baffle Construction | — | Continuous Baffles |
| Zipper Type | — | Full Length YKK |
What our reviewers liked and didn't
Ultima Thule -20
- Retains insulation when completely soaked
- Extreme durability, built to last a lifetime
- Reliable warmth in sub-zero temperatures
- USA-made, robust construction
- Excellent for expedition-level cold
- Very heavy and bulky
- Not suited for backpacking where weight is critical
- Less comfortable than some modern bags
- Price point is a significant investment
Puma GWS -25°F
- Unmatched warmth for its weight and temperature rating
- Superior 850+ fill power goose down insulation
- Effective Gore Windstopper shell protects against wind and moisture
- Continuous baffles allow down redistribution for customizable warmth
- Excellent draft collar and tube seal in heat
- Exceptional long-term durability and craftsmanship
- High initial cost is a significant investment
- Overkill for anything but extreme cold conditions
- Bulky even when compressed, takes up substantial pack space
- Requires careful storage to maintain loft and longevity
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