Here is how these two sleeping bags compare on the numbers. They score within a hair of each other, so it comes down to the details below.
| Feathered Friends Petrel UL 10 | Feathered Friends Lark YF 10 | |
|---|---|---|
| GearScore | 84✓ | 83 |
| Comfort rating | 20 °F | 20 °F |
| Weight | 29.8 oz✓ | 2 lb 1.4 oz |
| Warmth-to-weight | 5.9 /100g✓ | 5.3 /100g |
| Packed size | 11.0 L | 11.0 L |
| Fill power | 950 FP✓ | 900 FP |
| Price | $669 | $639✓ |
| Fill | Down | Down |
| Style | Bag | Bag |
| Shape | Mummy | Mummy |
Highlighted cells mark the better spec: Petrel UL 10 in blue, Lark YF 10 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 Petrel UL 10 against the Feathered Friends Lark YF 10 is a study in priorities. They are close enough that this really is about which handful of specs you weight most.
The Petrel UL 10 is 4 oz lighter, stronger on warmth-to-weight, and higher fill power (950 vs 900). The Lark YF 10 is $30 cheaper. Their GearScores land within a couple of points (84 vs 83), so neither runs away with it.
Pick the Petrel UL 10 if you care most about low weight and warmth-to-weight, which makes it the better call for counting grams on long miles. Pick the Lark YF 10 if price matter more to you, or you are focused on getting the most for your money.
The Feathered Friends Petrel UL 10. It is 4 oz lighter than the Lark YF 10.
The Feathered Friends Petrel UL 10. It is stronger on warmth-to-weight than the Lark YF 10.
They are nearly tied at 84 and 83 on the default algorithm, so re-weight the score to your own priorities to break the tie.
It depends on your priorities. Go with the Petrel UL 10 for low weight, or the Lark YF 10 for price. The spec table above shows exactly where each wins.