Here is how these two sleeping bags compare on the numbers. Both are solid; the right one depends on the specs you care about most.
| Feathered Friends Hummingbird UL 20 | Rab Mythic Ultra 20 | |
|---|---|---|
| GearScore | 87✓ | 68 |
| Comfort rating | 30 °F | 28 °F✓ |
| Weight | 23.9 oz | 21.3 oz✓ |
| Warmth-to-weight | 5.9 /100g | 7.0 /100g✓ |
| Packed size | 9.0 L | n/s |
| Fill power | 950 FP✓ | 900 FP |
| Price | $639 | $625✓ |
| Fill | Down | Down |
| Style | Bag | Bag |
| Shape | Mummy | Mummy |
Highlighted cells mark the better spec: Hummingbird UL 20 in blue, Mythic Ultra 20 in amber. A blank spec is never counted as a win. A lower comfort rating in °F means a warmer bag, so the warmer bag takes that row. GearScore is the overall rating (0 to 100); re-weight it on the full bag comparison. Prices are current MSRP.
The Feathered Friends Hummingbird UL 20 against the Rab Mythic Ultra 20 is a study in priorities. The Hummingbird UL 20 wins on fill power, and the Mythic Ultra 20 pushes back on warmth and low weight.
The Hummingbird UL 20 is higher fill power (950 vs 900). The Mythic Ultra 20 is warmer (rated 28°F vs 30°F), 3 oz lighter, and stronger on warmth-to-weight. On the default GearScore the Hummingbird UL 20 leads 87 to 68.
Pick the Hummingbird UL 20 if you care most about fill power, which makes it the better call for your priorities. Pick the Mythic Ultra 20 if warmth and low weight matter more to you, or you are focused on colder nights and shoulder-season trips.
The Rab Mythic Ultra 20. It is warmer (rated 28°F vs 30°F) than the Hummingbird UL 20.
The Rab Mythic Ultra 20. It is 3 oz lighter than the Hummingbird UL 20.
The Feathered Friends Hummingbird UL 20, 87 to 68 on the default algorithm. You can re-weight the factors to match your trip.
It depends on your priorities. Go with the Hummingbird UL 20 for fill power, or the Mythic Ultra 20 for warmth. The spec table above shows exactly where each wins.