The REI Co-op Magma 15 is a down bag rated to a standardized comfort of 21°F, weighing 2 lb 3.6 oz. It uses 850-fill-power down, and packs to 8.0 L, starts at $399.
GearScore breakdown
How this bag earns its 85 on the default algorithm, factor by factor
Have specific needs in mind — winter warmth, ultralight backpacking, or a bag on a budget? Rank this bag against every other on your own custom scoring algorithm.
Open the full bag comparison →Specifications
Temperature & provenance
We score warmth on the lab Comfort rating, the temperature this bag keeps a cold sleeper comfortable, and we use it exactly as published.
| Style: | Bag |
|---|---|
| Shape: | Mummy |
| Fill: | Down |
| Insulation: | 850FP goose down |
| Fill power: | 850 FP |
| Fill weight: | 23.3 oz660 g |
| Weight: | 2 lb 3.6 oz1.01 kg |
| Packed volume: | 8.0 L |
| Warmth-to-weight: | 4.9 /100g |
| Price per warmth: | $8 /warm |
How scoring works
The same GearScore engine the comparison pages use. This is the default weighting; open the full comparison to re-weight it around your trip.
GearScore blends published specs into one 0 to 100 number. Warmth (a standardized comfort rating) is a "good enough" gate; weight and packed size score on a sliding scale. Price and fill power are levers presets turn on.
Customize on the full comparison →- Sufficiency
- Only needs to be good enough. Warmth works this way: clear your target temperature and you're set, extra warmth adds no points.
- Monotonic
- More (or less) is always better. Lighter beats heavier and smaller packs beat bigger, so they score on a sliding scale.
- Preference
- Style, fill, and shape are personal preference, never scored. They only filter the list.