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#6 on this list
Sonic -20
Nemo
Thermo Gills let you dump heat without opening the bag. The best-ventilating winter bag made.
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#7 on this list
CWM -40
Marmot
The classic deep-cold workhorse. Overbuilt draft tubes and a full-length two-way zip.
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Specs side by side
| Spec | Sonic -20 | CWM -40 |
|---|---|---|
| Temperature Rating | -20°F (-29°C) | — |
| Insulation Type | 800 Fill Power Hydrophobic Down | — |
| Shape | Mummy | — |
| Ventilation | Thermo Gills | — |
| Primary Use | Winter camping, mountaineering | — |
| Maker | — | Marmot |
| Model | — | CWM -40 |
| Temp Rating | — | -40°F (-40°C) |
| Insulation | — | 800 Fill Power Goose Down |
| Shell Fabric | — | Pertex Quantum |
| Zipper | — | Full-length, Two-way |
What our reviewers liked and didn't
Sonic -20
- Thermo Gills allow unmatched temperature regulation
- Excellent warmth for its rating, even in damp conditions
- Generous internal space for comfortable movement
- High-quality hydrophobic down insulation
- Reinforced, waterproof footbox
- Not the absolute lightest -20°F bag available
- Higher price point than basic winter bags
CWM -40
- Uncompromising warmth in extreme cold
- Excellent draft management and insulation
- Highly durable shell and zipper construction
- Generous interior space for layering
- Proven track record in harsh conditions
- Heavy and bulky compared to less extreme bags
- Significant investment
- Overkill for temperate winter use
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