The Warmest Lab-Rated Bags Under Two Pounds
Two constraints, applied in order. First, the item has to publish a lab comfort figure — not a number the marketing department picked, an ISO 23537 or EN 13537 comfort rating measured on a mannequin. Second, it has to weigh under two pounds. What survives both is a short list, and that is the point: most of the bags people call ultralight publish no lab rating at all, so there is nothing to rank them by except trust.
How this list is orderedRanked by published ISO or EN comfort rating, coldest first, among bags and quilts under 32 oz that publish one at all. 7 entries qualify.
- 1
Sea to Summit
Sea to Summit Spark 15
28 °F comfort
1 lb 9.7 oz · ~$549 · Backpacking bag
Sea to Summit is one of the few brands that prints both ISO numbers next to each other, and the Spark 15 is the clearest illustration on this site of why that matters: the bag is sold as a 15, the lab limit is 16 °F, and the lab comfort figure is 28 °F. Twenty-eight is the number a cold sleeper should plan around, and it is thirteen degrees off the name. Everything else about the bag is excellent — 850-fill goose down, a 10-denier shell, a half-length zip to save weight, and 25.7 ounces total with nearly 17 ounces of that being down, which is one of the best fill-to-total ratios in the catalogue.
- 2
REI Co-op
REI Co-op Magma 15
28 °F comfort
1 lb 12.2 oz · ~$389 · Backpacking bag
REI revised the Magma 15 for 2026, and the new bag is a different proposition from the one most reviews describe: 850-fill goose down, 15.9 ounces of it, in a Pertex 15-denier shell, for 28.2 ounces total — about six ounces lighter than the previous version and $10 cheaper at $389. The ISO figures moved with it: a 28 °F comfort rating and a 16 °F lower limit, where the old bag tested to 21 and 9, and REI now prints 16 °F as the temperature rating even though the name still says 15. Read it as a lighter, cooler bag than its reputation: the limit sits within a degree of the name, but the comfort figure a cold sleeper should plan around is 28.
- 3
Therm-a-Rest
Therm-a-Rest Parsec 20
29 °F comfort
1 lb 13 oz · ~$470 · Backpacking bag
The Parsec is the lightest hooded mummy Therm-a-Rest makes, and one of the more honestly named bags here — it is called a 20 and it tests to a 29 °F comfort figure and an 18 °F limit, a nine-degree gap that only the Marmot Trestles Elite Eco beats among the 20-degree bags in this catalogue. Seventeen ounces of 900-fill duck down inside a 20-denier recycled shell gets the whole bag to 29 ounces. The zoned baffles put more down on top and less underneath, on the correct theory that the down you lie on is doing nothing, and the shoulder girth is a generous 62 inches for a bag this light.
- 4
Therm-a-Rest
Therm-a-Rest Vesper 20 Quilt
32 °F comfort
1 lb 3 oz · ~$460 · Quilt
Nineteen ounces, 900-fill goose down, a 10-denier shell and an EN comfort figure of 32 °F. The Vesper is one of the very few quilts from a mainstream brand that publishes a lab rating at all, and the number it publishes is worth reading carefully: a bag called a 20 that tests to a 32 °F comfort rating is a bag most people will feel cold in at 20. That is not a Therm-a-Rest problem, it is what the 20-degree label has always meant, and the Vesper is one of the few products honest enough to show its working. The SynergyLink straps are the good kind — they let the quilt float rather than pinning it flat.
- 5
Therm-a-Rest
Therm-a-Rest Corus 20 Quilt
32 °F comfort
1 lb 10 oz · ~$310 · Quilt
The Vesper's argument made in cheaper materials: same shape, same straps, same EN comfort rating of 32 °F, but 650-fill duck down inside a 20-denier shell instead of 900-fill goose down inside a 10. That costs seven ounces and saves $150, which for most weekend backpackers is the right side of the trade. The thicker shell is also more forgiving of the way quilts actually get used — dragged half-off the pad, sat on at breakfast, stuffed wet.
- 6
Sea to Summit
Sea to Summit Ember 30 Quilt
39 °F comfort
1 lb 3.2 oz · ~$414 · Quilt
One of three quilts in this catalogue with a published lab comfort figure, and the only one tested to the current ISO 23537 standard rather than the older EN 13537 — 30 °F limit, 39 °F comfort, with the limit landing exactly on the number in the name. Nineteen ounces of 850-fill down that zips into a closed footbox for a cold night and opens flat into a blanket for a warm one. Sea to Summit's ratings discipline is the reason to buy it rather than a cottage quilt at the same price: you know what you are getting before you sleep in it.
- 7
Exped
Exped Ultra 30
43 °F comfort
1 lb 6.5 oz · ~$400 · Backpacking bag
Tied for the widest honesty gap in this catalogue, and the reason the gap is worth measuring at all: this bag is sold as a 30 and its published ISO comfort figure is 43 °F. Thirteen degrees. Exped is not hiding it — they print comfort, limit and extreme side by side on the product page, which is more than most brands do — but a buyer reading the name and not the table will be cold on a 35-degree night. Taken on its real numbers it is a very good summer bag: 22.5 ounces, 850-fill RDS down, a 10-denier recycled shell and a shoulder girth of 58 inches with a wide option at 64.
The top three, in full
Sea to Summit
Sea to Summit Spark 15
Sea to Summit is one of the few brands that prints both ISO numbers next to each other, and the Spark 15 is the clearest illustration on this site of why that matters: the bag is sold as a 15, the lab limit is 16 °F, and the lab comfort figure is 28 °F. Twenty-eight is the number a cold sleeper should plan around, and it is thirteen degrees off the name. Everything else about the bag is excellent — 850-fill goose down, a 10-denier shell, a half-length zip to save weight, and 25.7 ounces total with nearly 17 ounces of that being down, which is one of the best fill-to-total ratios in the catalogue.
Best for: Backpackers who want the honest number before they buy
Full spec sheet
REI Co-op
REI Co-op Magma 15
REI revised the Magma 15 for 2026, and the new bag is a different proposition from the one most reviews describe: 850-fill goose down, 15.9 ounces of it, in a Pertex 15-denier shell, for 28.2 ounces total — about six ounces lighter than the previous version and $10 cheaper at $389. The ISO figures moved with it: a 28 °F comfort rating and a 16 °F lower limit, where the old bag tested to 21 and 9, and REI now prints 16 °F as the temperature rating even though the name still says 15. Read it as a lighter, cooler bag than its reputation: the limit sits within a degree of the name, but the comfort figure a cold sleeper should plan around is 28.
Best for: Backpackers who want a lab-rated 850-fill bag under $400 from a shop that takes returns
Full spec sheet
Therm-a-Rest
Therm-a-Rest Parsec 20
The Parsec is the lightest hooded mummy Therm-a-Rest makes, and one of the more honestly named bags here — it is called a 20 and it tests to a 29 °F comfort figure and an 18 °F limit, a nine-degree gap that only the Marmot Trestles Elite Eco beats among the 20-degree bags in this catalogue. Seventeen ounces of 900-fill duck down inside a 20-denier recycled shell gets the whole bag to 29 ounces. The zoned baffles put more down on top and less underneath, on the correct theory that the down you lie on is doing nothing, and the shoulder girth is a generous 62 inches for a bag this light.
Best for: Three-season backpackers who want a hooded bag near quilt weight
Full spec sheet