REI Co-op
REI Co-op Magma 15
No citable owner-review average published for this one, so no stars.
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.
Label against lab
Sold as a 15 °F bag; its ISO 23537 comfort rating is 28 °F, which is 13 °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 4 pad underneath it.
Specifications
Highlights
Features
- ISO or EN rated
- Hydrophobic down
- Draft collar
- Half-length zipper
What it does well
- Publishes both ISO figures, and the 16 °F lower limit lands within a degree of the name — the comfort figure is the one to plan around.
- 28.2 ounces with 15.9 ounces of 850-fill goose down, in the same ISO 28/16 bracket as Sea to Summit's Spark 15 for $160 less.
- Pertex 15-denier shell and lining, water-resistant down, a 63-inch shoulder girth and a 5.2-litre compressed volume — REI publishes all of it.
- Sold through a co-op with a real returns policy, which matters for a bag whose fit you cannot judge in a photograph.
What it costs you
- The 28 °F comfort figure is thirteen degrees off the 15 in the name — tied for the widest gap in this catalogue — so a cold sleeper should treat it as a high-20s bag.
- Reviews written before the 2026 revision describe a heavier, warmer bag; check the date before trusting a figure.
- Two lengths and one width, in left or right zip; there is no built-to-order width or overfill option.
Those two lists are drawn from REI Co-op’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
Distilled from owner discussions and long-term published reviews, not from anything measured here.
The Magma has become the reference point in budget sleeping-bag discussion, and for an unusual reason: it is the bag people use to explain how temperature ratings work. Owners quoting ISO figures at each other reach for it because it is the well-known bag that publishes both — though the 9 °F limit and 21 °F comfort they quote are the previous version's; REI's 2026 revision is lighter and tests to 16 and 28.
The technical praise is specific too. Owners describe the short box baffle construction, sewn about an inch deep with roughly four inches at mid-baffle, and compare it favourably with a respected cottage maker's approach. That is not the kind of detail people usually volunteer about a retailer-brand bag.
Owners say the same thing every time: wait for a sale, and if you are unsure about quilts, buy the quilt in the same line because you can return it.
What owners like
- It is the bag owners point at when someone asks for the best budget option, with the standing advice to buy it on sale.
- Owners cite the ISO figures directly and use it as the worked example of how the standard works — though the 9 °F limit and 21 °F comfort quoted in older discussion belong to the version sold through 2025; REI's 2026 revision tests to 16 and 28.
- The construction gets technical praise: short box baffles sewn about an inch deep with a four-inch mid-baffle, a design owners compare favourably to a well-regarded cottage maker's.
- The quilt in the same line gets recommended as a low-risk way to try a quilt, because a shop with a returns policy is behind it.
- Owners report REI-branded gear generally as good quality, with better available only at meaningfully higher cost.
Common complaints
- Tall owners note it adds real volume to heat, and a long version of a roomy bag is a lot of air for a cold sleeper.
- The best prices depend on sales, which owners treat as the normal way to buy it rather than as a bonus.
- Nothing about it is unusual, which is both why it gets recommended and why owners rarely enthuse.
Questions owners ask
What are the actual temperature ratings?
Is the construction any good for the price?
Should I wait for a sale?
Is the quilt in the same line worth a look?
REI Co-op Magma 15, head to head
Others in the same band
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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
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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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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