Sea to Summit Spark 15 vs Feathered Friends Swallow YF 20
In short: The Feathered Friends Swallow YF 20 costs $20 less; the Feathered Friends Swallow YF 20 is rated 8 °F colder on the figure each maker publishes; the Sea to Summit Spark 15 saves 3.5 oz; the Feathered Friends Swallow YF 20 carries the bigger loft budget at 15.1k cubic inches; only the Sea to Summit Spark 15 publishes a lab temperature rating at all.
| Spec | Sea to Summit Spark 15 | Feathered Friends Swallow YF 20 |
|---|---|---|
| Approx. price | ~$549 | ~$529 |
| ISO comfort | 28 °F | not published |
| ISO limit | 16 °F | not published |
| Rating on the label | 15 °F | 20 °F |
| Honesty gap | 13 °F | — |
| Rating standard | ISO 23537 | manufacturer |
| Weight | 1 lb 9.7 oz | 1 lb 13.2 oz |
| Warmth per ounce | 1.25 °F/oz | — |
| Fill | 850 fill power down | 900 fill power down |
| Fill weight | 16.9 oz | 16.8 oz |
| Loft budget | 14.4k in³ | 15.1k in³ |
| Shape | mummy | mummy |
| Shoulder girth | not published | 59 in |
| Zipper | half | full |
| Shell fabric | 10D nylon | Pertex YFuse |
| Hydrophobic down | Yes | No |
| Packed size | 6.8 L | 9 L |
Shaded cells mark the row where one has a measurable advantage. Weight, thickness, girth and shape are left unshaded on purpose: heavier is sometimes tougher, wider is sometimes warmer, and calling a winner on those would be an opinion dressed as a measurement.
What each one does well, and costs you
Sea to Summit Spark 15
- Publishes the ISO comfort figure (28 °F) as well as the limit (16 °F), which most of this catalogue does not.
- 16.9 ounces of 850-fill down inside a 25.7-ounce bag — about two-thirds of the total weight is insulation.
- The half-length zip saves real weight over a full zip and still vents enough for a warm night.
- 6.8 litres compressed is small for a hooded 15-degree bag.
- Non-PFAS Ultra-Dry down treatment, RDS-certified.
- $549 is at the top of the mainstream price band, and the cottage makers do 20-degree quilts for less.
- The half zip cannot be opened into a blanket and makes getting in on a cold night more of a wriggle.
- 10-denier shell is delicate; this is not a bag to use as a groundsheet or a couch.
- No shoulder girth published, so the fit is hard to judge without trying it.
Feathered Friends Swallow YF 20
- Publishes shoulder, elbow, hip and footbox girth — the most detailed fit data of any bag in this catalogue.
- 900+ fill-power Muscovy down, a grade only two other items here use.
- 16.8 ounces of down inside a 29.2-ounce bag, with a NetPlus recycled-nylon lining.
- Sewn in Seattle, with the repair and re-loft service that implies.
- Available as a 20 or a 30 on the same pattern, so the fit carries across temperatures.
- No ISO or EN rating published.
- $529 for the Regular, and the ultralight Hummingbird above it is another $110.
- The down is not hydrophobic-treated.
- Two lengths and one girth; the Wide fit lives on a different model.