Therm-a-Rest Boost 650 Sleeping Bag Review
A semi-rectangular down bag for backpackers who prioritize comfort and size-inclusivity
August 7, 2026
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Our verdict
The Therm-a-Rest Boost 650 is a bag made for car campers and backpackers alike who are looking for comfort and a size-inclusive fit. The semi-rectangular bag is made with 650-fill duck down and can convert to a more traditional mummy shape with the WarmZip center zipper. It's the most size-inclusive and most comfortable down backpacking bag we've tested
I tested the Boost 650 20°F/ -6°C in the Regular Wide size over the course of three months: from early spring overnights in the high desert of Southern Idaho to early summer in Southern Oregon, along with several nights in the Sawtooth National Forest in mid-summer. I tested the bag in temperatures as low as 28°F and up to the upper 40s. I am a side sleeper and someone who is generally warm once in the tent, with the exception of my cold feet—an ongoing struggle I’ve faced with nearly every bag I’ve tested. I’m also a size 18/20 in clothing, which can sometimes be challenging to find a mummy-style bag made for backpacking that fits without being too tight. With the Therm-a-Rest Boost 650, the vast majority of my needs as a sleeper and camper were met.
In the field, the bag stands out as the softest and most comfortable bag I’ve tested, and I looked forward to cozying into it after a long day of hiking and paddling. It’s also extremely size inclusive, with the Regular Wide size fitting me with many inches to spare. The bag is bulky and heavier than what most weight conscious backpackers would prefer, with the Boost 650 in the 20°F weighing 3 lbs 5 oz.
It’s also important to note that real-world temperature performance not aligning with the stated rating is a recurring theme in user reviews and reflects my own experience from the field, where I felt surprisingly chilled on some nights when temperatures dipped to their lowest.
Therm-a-Rest Boost 650
The Therm-a-Rest Boost 650 straddles the line between a backpacking sleeping bag and a camping sleeping bag. For more of our backpacking favorites, check out our Best Backpacking Sleeping Bags or Best Backpacking Quilts guides; for more of our camping favorites, check out our Best Camping Sleeping Bags guide.
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Therm-a-Rest Boost 650 Specifications
| Short | Short Wide | Regular | Regular Wide | Long | Long Wide | |
|---|---|---|---|---|---|---|
| Price | $259.95 | $279.95 | $299.95 | $319.95 | $339.95 | $359.95 |
| ISO Lower Limit | 32°F | 32°F | 32°F | 32°F | 32°F | 32°F |
| ISO Comfort | 41°F | 41°F | 41°F | 41°F | 41°F | 41°F |
| Weight | 1 lb 9 oz | 2 lbs 2 oz | 2 lbs 2 oz | 2 lbs 8 oz | 2 lbs 7 oz | 2 lbs 14 oz |
| Fill weight | 12 oz | 1 lb | 14 oz | 1 lb 3 oz | 1 lb | 1 lb 5 oz |
| Short | Short Wide | Regular | Regular Wide | Long | Long Wide | |
|---|---|---|---|---|---|---|
| Price | $299.95 | $319.95 | $339.95 | $359.95 | $379.95 | $399.95 |
| ISO Lower Limit | 20°F | 20°F | 20°F | 20°F | 20°F | 20°F |
| ISO Comfort | 32°F | 32°F | 32°F | 32°F | 32°F | 32°F |
| Weight | 2 lbs 4 oz | 2 lbs 13 oz | 2 lbs 11 oz | 3 lbs 5 oz | 3 lbs 1 oz | 3 lbs 13 oz |
| Fill weight | 1 lb 4 oz | 1 lb 11 oz | 1 lb 7 oz | 2 lbs | 1 lb 10 oz | 2 lbs 4 oz |
| Compressed volume | 7.1 L | 7.6 L | 8.7 L | 9.4 L | 10.9 L | 10.1 L |
| Stuff sack size | 18 x 6.5 in | 18 x 6.5 in | 20 x 7.5 in | 20 x 7.5 in | 20 x 7.5 in | 20 x 7.5 in |
| Fits up to | 66 in | 66 in | 72 in | 72 in | 78 in | 78 in |
| Shoulder girth | 63 in | 75 in | 64 in | 76 in | 65 in | 77 in |
| Hip girth | 59 in | 73 in | 60 in | 74 in | 61 in | 75 in |
All variants
Shape: Semi-rectangular (converts to mummy via WarmZip)
Fill: 650-fill-power duck down, PFAS-free hydrophobic, RDS-certified
Shell: 20-denier 100% recycled nylon ripstop
Lining: 20-denier 100% recycled nylon ripstop
Zipper location: Left
WarmZip center zipper: Yes (converts shape; adds up to 10°F/6°C — not EN/ISO rated)
Arm holes: Yes (zippered, bilateral)
2-way side zipper: Yes
Draft collar: Yes
Draft tube: Yes (along entry zipper)
Hood: Yes, cinchable
Interior pocket: Yes (open top)
Stuff sack included: Yes (compression sack)
Storage sack included: Yes
Sustainability: GRS-certified shell and liner (100% recycled nylon), RDS-certified down, PFAS-free DWR
Best for
Backpackers who camp and campers who backpack, and who value a comfortable bag with an abundance of features
Milder temperatures and shoulder seasons where lows are less likely to get closer to the temperature rating on the bags
Campers who plan to use the bag in dry conditions or only mildly wet conditions
Campers and backpackers who don’t mind carrying a heavier sleeping bag
Comparison table
| Feature | Therm-a-Rest Boost 650 20F | NEMO Disco 15 Endless Promise | REI Co-op Magma 30 | Kelty Cosmic Down 20 | Sea to Summit Ascent 15 |
|---|---|---|---|---|---|
| Price | $300 - $400 | $300 - $350 | $349-$359 | $180 - $210 | $449 - $479 |
| Temperature rating | 20F | 15F | 30F | 20F | 15F |
| Fill power | 650 | 650 | 850 | 550 | 750+ |
| Shape | Semi-rectangular | Semi-rectangular | Mummy | Mummy | Mummy |
| Weight (regular) | 2 lbs 11 oz | 2 lbs 11 oz | 1 lb 8.4 oz | 2 lbs 7 oz | 2 lbs 4 oz |
| Compressed volume | 8.7L | 6.4L | 4.3L | 10.7L | 7.5L |
| WarmZip / shape change | ✔ | -- | -- | -- | -- |
| Arm holes | ✔ | -- | -- | -- | -- |
| Wide sizing available | ✔ | ✔ | ✔ | -- | -- |
| ISO tested | ✔ | ✔ | ✔ | ✔ | ✔ |
What we liked
The inclusive fit, with both the WarmZip open and closed
The integrated arm holes, while not a feature I’ve ever explicitly desired in a bag, are more fun and useful in practice than I had originally anticipated
Comfortable and adjustable overall fit
What could be better
Cold spots around the feet when the night was coldest—either from the bag’s temperature rating not aligning with real-world experience, or because there was so much room around my feet that the bag was slightly too big around me to heat me efficiently, or even a combination of both
Not the lightest bag at 3 lbs 5 oz in the Regular Wide, though the Regular (non wide) is slightly lighter at 2 lbs 11 oz
The 650-fill down is not as light and lofty as bags with higher fill power, like the REI Magma 30
The additional bulk makes the bag less packable when space is at a premium, so not ideal for lightweight backpackers
How we tested
I tested the Therm-a-Rest Boost 650 over a dozen nights in three major locations in the Intermountain West and Pacific Northwest, with temperatures ranging from the 20°s to the 40°s. Our tent was pitched on primarily mountainous terrain during testing, along with the sagebrush-covered ground of the high desert.
I am a side sleeper who is usually warm except for my feet. I slept in the bag inside the walls of a Big Agnes Blacktail 3 while backpacking and a REI Basecamp 4 when car camping, during both rainy and clear nights. During my testing I used two sleeping pads: the REI Co-op Helix (R-value of 4.9) and the NEMO Quasar 3D (R-value of 3.3), which is now discontinued—though a similar pad, the NEMO Eclipse, is available. Both pads are in wide sizes, and are 3 inches (REI) and 4 inches (NEMO) thick.
We also tested this sleeping bag alongside others in our Best Backpacking Sleeping Bags and Best Camping Sleeping Bags guides to directly compare features and performance.
Performance in the field
Warmth and temperature accuracy
The Therm-a-Rest Boost 650 isn’t the warmest bag, nor does it purport to be, but in field testing we did find it to have cold spots on nights where temperatures were in the mid 40s when my partner slept with a 30°F bag and was completely warm.
I am not a cold sleeper overall, but do tend to get cold in my feet which is where I felt the cold spots during our testing; so those who don’t struggle with cold feet may experience less chill than I do. Despite my predisposition to frosty feet, I have tested other bags with similar temperature ratings that didn’t leave my feet cold.
From testing, I would put the comfort rating at closer to 30-35°F for the 20°F version that I tested. I did find the WarmZip system to increase warmth when closed: although it was difficult to measure by how much in the field, I did feel a discernable increase when used versus nights when it’s completely unzipped.
WarmZip system in practice
The Boost 650’s WarmZip system is a useful feature both for fit and comfort along with thermal regulation and increasing warmth. In the dark tent at 1 am after returning from using the bathroom and my hands were freezing I was thankful for the wide zipper that made it easy to zip closed. In testing, it snagged a few times upon opening and closing a few times, but nothing impossible to unsnag or too distracting.
The WarmZip does indeed boost the overall warmth of the bag. On night one of using the Boost 650 I left the WarmZip fully unzipped, and was more comfortable the following night when the WarmZip was closed, even though the temperature was approximately 2 degrees lower than the previous night. I’ve replicated this in other testing locations as well, finding that the WarmZip does keep me warmer when closed than nights where we don’t use it.
Comfort and sleep position
The Therm-a-Rest Boost 650’s semi-rectangular shape is my favorite shape of bag to sleep in, feeling less constrictive and tight than a traditional mummy bag without the huge bulk of the typical rectangular style car camping bags.
I found it similar to the experience of using a NEMO Disco and the spoon shape they use for many of their bags. The Boost is even roomier than the NEMO both in actual measurements and in practice. In the NEMO, I still felt slightly snug despite the wide width I tested, while the Boost 650 is spacious in comparison. Even with the WarmZip closed, the additional inches in width and size make the WarmZip feel much roomier in practice.
This sleeping bag is the best-fitting bag for my size 18/20 body that I take backpacking. While measuring and testing for fit is vital and all bodies are different, I would say that a person who is 2-3 sizes larger than me could comfortably fit into the Regular Wide size, a rare feature (that shouldn’t be rare at all) to find in bags suitable in weight, materials, and design for overnight backpacking trips. The Regular Wide measures 76 inches in shoulder girth with 74 inches of hip girth, and even with the WarmZip closed and the bag in the mummy shape, I never felt constricted or confined.
Arm holes
I loved the arm holes, a feature that was fun to find and even more fun to use. I often wake early when camping and backpacking, and will lay reading while I wait for the sun to rise. With traditional mummy bags, I am not able to move my arms to easily or comfortably read while on my side, and is impossible to do while sleeping on my back as well. With the Boost’s arm holes, I can do all of these things and more, including reaching for the tent door zipper, writing in a journal, and all other manner of things I couldn’t do with previous bags without fully removing my arms and shoulders from the bag.
The holes also act as vents, and I appreciated being able to close one while keeping the other open for finding my most comfortable sleeping temperature. At first I couldn’t easily find them at night, but after using them once or twice I was able to easily find and unzip them in the dark.
Packability and weight in practice
The Boost 650 doesn’t compress as well as other bags I have used, though it is comparable in compressed size and overall weight as the NEMO Disco, likely due to both bags having 650 fill power. The REI Magma 30, which I’ve also used frequently in the past year or so, is also bulky when stuffed into a pack. The weight difference is noticeable on the trail though, with the Magma weighing almost two pounds less than the Boost 650.
Durability
The Therm-a-Rest Boost 650 is made of 20-denier 100% recycled nylon ripstop fabric, and both the shell and liner are treated with PFAS-free water repellent finish, made to prevent water from passing through the fabric. In the field, I didn’t notice that the shell was susceptible to snagging or ripping, even when I carelessly tossed it over a trunk with sharp branches to air out before I put it away.
The shell itself was made for softness and comfort, which seem to be stronger features than overall durability. The soft shell means that I would likely not choose the Boost for multiple nights spent sleeping on rough granite or by a sharp sagebrush directly under the stars. Although I didn’t observe any tearing, I did notice after the fourth use that the occasional feather would be floating in the tent after moving or disturbing the bag. As I used the bag more, the amount of feather loss increased slightly until I found it in a location I hadn’t noticed getting snagged or brushed against anything abrasive: a pinprick sized hole where feathers were escaping.
Features
Semi-rectangular shape with WarmZip center zipper (converts to mummy)
The Therm-a-Rest Boost 650 feels like two bags in one, both a roomy semi-rectangular bag with inches to spare and space to spread out, and a more compact mummy bag that brings extra warmth without feeling as constrictive as other mummy bags I’ve used.
WarmZip adds up to 10°F / 6°C to warmth (not EN/ISO rated)
Over repeated use, I observed that WarmZip does add extra warmth when closed compared to evenings with similar temperatures where the WarmZip was left unzipped. The WarmZip zipper is centered on the bag’s outer shell, going from about mid-chest down to the footbox.
Bilateral zippered arm holes
The bilateral zippered arm holes are large enough to accommodate most arm sizes, fitting broad shoulders comfortably and without restrictive movement. They are secured with a comfortable and wide zipper and a 2-inch (approximately) long, easy to grab drawstring.
650-fill-power RDS-certified hydrophobic duck down
The Boost 650 is made with 650-fill power RDS (Responsible Down Standard) hydrophobic duck down made to repel occasional dampness, but is not as lofty or compressible as bags with higher fill power. It does provide consistent warmth on milder nights
Zoned insulation
The zoned insulation is visible in the design of the bag itself, placing down around your core and top for warmth where it counts. With less insulation on the bottom, those with cold feet and lower extremities may experience more chill.
PFAS-free DWR on shell and liner
The Therm-a-Rest Boost 650 is treated with a PFAS-free Durable Water Repellent (DWR) finish, acting as a preventive for water penetrating through the shell and into the down fill.
20-denier 100% recycled nylon shell and lining (GRS-certified)
The bag’s shell is made of 20-denier 100% recycled nylon, as well as the lining, making for a silky soft feel that is similar to sinking into sheets at home.
YKK anti-snag zipper pulls on all zippers
The zipper pulls are a strong feature on the Boost, making for easy closure and opening without snagging and tearing.
Puffy draft collar
The draft collar is thick and plush, so thick it feels like a second pillow. The lofty collar can be cinched tight to prevent drafts.
Draft tube along entry zipper
The draft tube at the entry zipper creates warmth when securely closed, adding to the many features created for comfort.
Cinchable hood
The mummy style hood is wider and somewhat shallow, creating a tighter fit that also retains warmth on chilly nights.
Large interior STASH pocket (open top)
The Boost 650’s large interior stash pocket, located around the inside chest of the bag, fits a larger Android or a standard-sized iPhone with ease.
Compression sack and storage sack included
Down fill requires extra care during storage, and Therm-a-Rest supports this care by providing a large mesh stuff sack for regular storage and a compression sack for backpacking and other activities where saving space is necessary.
Inclusive sizing
The Therm-a-Rest Boost 650 line features a wide variety of size offerings: Short, Short Wide, Regular, Regular Wide, Long, Long Wide, with generous cuts among the wide widths for many different body shapes and sizes.
Temperature variants
Boost 650 32°F
Best for three-season backpacking in mild to moderate conditions; lighter and more packable than the 20°F.
Boost 650 20°F
Best for colder shoulder-season trips; heavier and bulkier but handles harder frosts. (In our experience we found the comfort rating of the 20°F to be closer to 30°F.)
Should you buy the Therm-a-Rest Boost 650?
Buy if:
You prioritize comfort, whether that be through the roomy design or the silky exterior
You love a bag with features like arm holes and the WarmZip
You want a bag for camping and backpacking but don’t mind the weight or bulk
Skip if:
You’re looking for a lean and lightweight bag for backpacking trips
You sleep cold
You’re looking for a straightforward camping bag at a lower price
Where to buy
The Therm-a-Rest Boost 650 Sleeping Bag is a popular gear item, so you have options when it comes to retailers. Here are some of the pros of the retailers.
REI
Pros: 100% satisfaction policy for 1 year; 10% dividend for members.
Amazon
Pros: Free 2-day shipping with Amazon Prime membership (can be same-day delivery in major metropolitan cities)
Backcountry
Pros: Frequent sales for Expedition Perks members (free to join), fast shipping, Gearhead chat customer service is excellent
Advice on where to buy
In general for gear, we recommend purchasing from a place with easy or free returns, like REI. If your funds allow, many people find it is faster to order two sizes and return whichever one didn't fit as well. Additionally, check reviews to see whether other users recommend sizing up or down.
Therm-a-Rest Boost 650 FAQ
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Yes! According to Therm-a-Rest, the WarmZip adds up to 10°F/6°C to the Boost’s temperature rating. In practice, the difference was real and repeatable – we noticed an immediate difference in warmth when the zipper was closed. It's worth noting this figure isn't EN/ISO tested.
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The difference between the variants of the Boost 650 lies primarily in the temperature rating and the weight (both fill weight and down volume). Because of the additional down insulation, the 20°F variant is 3 lbs 5 oz in the Regular Wide, while the 32°F weighs 2 lbs 8 oz. The 20F is also bulkier and will take up more space in your pack.
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The Boost 650 is a dream for side sleepers, cut generously even in the non-wide widths.
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In our testing, we found the Boost 650 to generally run cold relative to its temperature rating. Plan your trips with a 10–15 degree buffer, or layer up with baselayers and wool socks when lows approach the rating.
Similar sleeping bags
Therm-a-Rest Boost 650 vs NEMO Disco Endless Promise
Price: $300 - $350
Temperature rating: 15F
Fill power: 650
Shape: Semi-rectangular
Weight: 2 lbs 11 oz
Both the Therm-a-Rest Boost 650 and the NEMO Disco Endless Promise seek to solve the problem that most backpacking sleeping bags face: the claustrophobic feel of a traditional mummy bag.
Both bags utilize 650-fill hydrophobic down, but the design, ventilation, and warming features may connect to different users. While the Boost 650 features the WarmZip center zipper, the Disco’s Thermo Gill chest vents offer ventilation without the additional inches of width that the WarmZip offers (and the NEMO Thermo Gills can’t double as arm holes, only vents).
The Therm-a-Rest is for hikers looking to center comfort and versatility, especially those who want as much room as possible in a backpacking bag or need the room because they have a larger body. The Therm-a-Rest is larger than the NEMO Disco, which fits more snugly than the Boost. Campers looking to prioritize sustainability and packability should turn to the Disco.
Learn more in our in-depth review of the NEMO Disco Endless Promise Sleeping Bag.
NEMO Disco Endless Promise
Men's
Women's
Therm-a-Rest Boost 650 vs REI Co-op Magma 30
Price: $349-$359
Temperature rating: 30F
Fill power: 850
Shape: Mummy
Weight: 1 lb 8.4 oz
For campers and backpackers who don’t mind a more traditional mummy shape, the REI Co-op Magma 30 is a similarly priced option that is much lighter in weight with higher, 850-fill power down. The streamlined mummy shape comes in wide widths, which felt close to the body without the constriction, and is wide enough for a 2X/3X clothing sized person to fit and turn without issue. The Magma 30 is better suited for backpacking due to its lower weight and higher fill power, but is equally usable and liveable around basecamp or when car camping.
Those who prefer to backpack and don’t need the additional space of the Boost 650 may prefer the Magma, while those prioritizing flexibility and space should turn to the Boost 650.
REI Co-op Magma 30
Why you should trust us / About the author
I am a former outdoor educator and camp professional who knows that choosing the right gear for your outdoor adventures can make or break your experience. I car camp down forest roads, backpack the Sawtooths and BLM land throughout Southern Idaho, and occasionally visit a developed national forest campground.
Through all of these settings I am a side sleeper who traditionally struggles to find sleeping bags that fit. I have tested bags and gear in rain, snow, and humid and dry conditions. Down sleeping bags are at the center of my core sleep system, and I appreciate that the extra effort that goes into caring for them can result in a reliably warm bag that lasts for years.
Find more of my work on my Treeline Review author page.
