Therm-a-Rest
Therm-a-Rest Boost 650 20
No citable owner-review average published for this one, so no stars.
Six sizes, three lengths in two widths, which is more fit choice than almost any other bag here offers and the reason the Boost is worth a look for anyone who has been cold in a standard mummy because they couldn't fill it — or trapped in one because they overfilled it. The Wide versions add eleven or twelve inches of shoulder girth, which is a genuinely different bag rather than a token option. The tradeoff is 650-fill down and 43 ounces in the Regular: heavy for backpacking, entirely reasonable for a bag that gets used a dozen nights a year.
Label against lab
Sold as a 20 °F bag; its EN 13537 comfort rating is 32 °F, which is 12 °F warmer than the name suggests. Plan around the comfort figure, not the label. Why the gap exists
At that temperature the pairing table wants at least an R 3 pad underneath it.
Size run
One product, 6 sizes. The headline numbers on this page describe the Regular.
| Size | Weight | Approx. price | Length | Shoulder girth |
|---|---|---|---|---|
| Short | 2 lb 4 oz | ~$300 | 73 in | 63 in |
| Short Wide | 2 lb 13 oz | ~$320 | 73 in | 75 in |
| Regular | 2 lb 11 oz | ~$340 | 80 in | 64 in |
| Regular Wide | 3 lb 5 oz | ~$360 | 80 in | 76 in |
| Long | 3 lb 1 oz | ~$380 | 85 in | 65 in |
| Long Wide | 3 lb 13 oz | ~$400 | 85 in | 77 in |
Specifications
Highlights
Features
- ISO or EN rated
- Hydrophobic down
- RDS down
- Draft collar
- Full-length zipper
- Wide option
- Recycled fabric
What it does well
- Six sizes across three lengths and two widths — a 76-inch shoulder girth in Regular Wide is a full foot more than a standard mummy.
- Publishes EN comfort (32 °F), limit (20 °F) and extreme (-9 °F) figures, and the per-size girth numbers alongside.
- 650-fill duck down is RDS-certified, PFAS-free and hydrophobic-treated.
- $340 for the Regular is mid-market for a down bag with a real lab rating behind it.
What it costs you
- 43 ounces in the Regular and 61 in the Long Wide — that is three and three-quarter pounds for the biggest size.
- Packs to 12.5 × 7.5 inches, which is a lot of a weekend pack's volume.
- 650-fill down buys loft by bulk, so the Wide sizes get heavy fast.
- As with every 20-degree bag here, the comfort rating is 32 °F; treat 20 as the survival end of the scale.
Those two lists are drawn from Therm-a-Rest’s published specifications and from reviews that measured them. They are not owner sentiment — anything owners said appears under its own heading below.
What owners say
No owner discussion has been collected for the Therm-a-Rest Boost 650 20 yet. The pros and cons above come from Therm-a-Rest’s published specifications and from reviews that measured them — nothing on this page claims owners said anything. How that works.
Therm-a-Rest Boost 650 20, head to head
Others in the same band
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The Parsec is the lightest hooded mummy Therm-a-Rest makes, and the one entry here where the marketing number and the lab number sit only nine degrees apart — it is called a 20 and it tests to a 29 °F comfort figure and an 18 °F limit, which is about as close to truth-in-labelling as the 20-degree class gets. 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.
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Mountain Hardwear
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A lot of down for the money: the Bishop Pass carries more fill than almost any bag at its price, at 650 fill power, and publishes an ISO comfort rating of 26 °F. Five and a half inches of measured loft in a 20-denier shell, with an expanded shoulder, hip and leg cut that Mountain Hardwear calls Performance Plus and most people would just call comfortable. At 37.4 ounces it is heavy for a 15-degree bag, and all of that weight is the low fill power buying loft through bulk.
Best for: Cold sleepers who want loft more than they want ounces
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Big Agnes
Big Agnes Torchlight EXP 20
Two zippered expansion panels run from shoulder to footbox and add five inches of girth on each side — ten inches in total — which makes this the only bag here whose fit you can change after you have bought it. Zip them shut on a cold night and it is a normal mummy; open them on a warm one and it is closer to a semi-rectangular bag. That is a genuinely good answer to the problem that a bag tight enough to be warm is too tight to sleep in. The trade is 40 ounces and a manufacturer-only 20-degree rating with no lab figure behind it.
Best for: Sleepers who want a mummy some nights and room on others
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