The Therm-a-Rest Boost 650 20 ($340) is a comfort-first sleeping bag that offers impressive versatility thanks to its spacious semi-rectangular design and unique “WarmZip” zipper, which toggles the bag’s shape between roomier and more thermally efficient configurations. Super-soft fabrics and thoughtful features (armholes!) round out the bag’s smart—but not overbuilt—layout. While too heavy and bulky for weight-conscious backpackers, the Boost is a fantastic option for car camping, travel, casual backpacking, or any activity during which comfort takes priority over ounces.
Warmth / Weight
Comfort
Features
Durability
Water Resistance
Sustainability
Temp Rating
32/20°F (ISO Comfort/Limit)
Weight
2 lb. 11 oz.
Fill
1 lb. 7 oz. of 650-fill down
Shell
20D nylon
Shoulder/Hip Girth
64/60 in.
Packed Volume
14.5L
Other Temps
32F
Pros
Cons
Therm-a-Rest Boost 650 20
For this season's top models, see our guide to the Best Backpacking Sleeping Bags.
The Therm-a-Rest Boost 650 20 delivers solid warmth overall, though it’s not winning any ultralight awards. At 2 pounds 11 ounces, it has an ISO-certified 20-degree Lower Limit; for comparison’s sake, the Therm-a-Rest Parsec 20 offers similar warmth (18˚F Lower Limit) for almost a full pound less (1 lb. 13 oz.). But if weight and bulk aren’t huge considerations, the Boost is coziness incarnate: Its zoned insulation places down where you want it most (on top and around your core), and the WarmZip allows you to toggle between a spacious, 20-degree semi-rectangular shape and a more thermally efficient mummy bag. To seal out drafts, just cinch tight the lofty draft collar and sink into the spacious hood.
During my month of testing in an unheated cabin in El Chaltén, Argentina, I slept comfortably in the Boost even when temperatures dipped into the mid-30s. On one particularly cold night (with snow falling outside, a rarity during summer in Patagonia), zipping up the WarmZip made an instant difference—I felt noticeably warmer, and the chills disappeared. On the flip side, when my sleeping loft heated up to nearly 70 degrees (Patagonian weather knows no bounds), I unzipped the Therm-a-Rest Boost 650 completely and used it as a blanket, something many traditional mummy bags with truncated zippers don’t allow.
If warmth-to-weight efficiency is your top priority, there are better options out there. The culprits are the Boost’s 650-fill down (which isn’t as lofty as 800-and-up fill powers in lighter backpacking sleeping bags) and its feature-heavy design. This makes it heavier than most 20-degree bags, and bulkier too: Even when using the included compression sack, the Boost filled the entire bottom of my 50-liter climbing pack, leaving no room for my tent to slip in side-by-side (which is how I typically like to pack). On the other hand, I found the Boost completely serviceable for travel. While packing for my month in Patagonia, I put it in its large storage sack and tucked it into the corner of my duffel without issue. So while this bag wouldn’t be my first choice for fast-and-light backpacking, it’s a wonderfully versatile option for travelers, car campers, and casual hikers looking for a cozy 20-degree bag, and could fit the bill for folks carrying larger backpacks (such as the Osprey Aura AG 65), especially if you’re the type to tote extra luxuries like a watermelon (true story).
The Therm-a-Rest Boost 650 is one of the roomiest and most comfortable backpacking sleeping bags I’ve ever tested, especially in its semi-rectangular configuration. With the WarmZip undone, the bag measures 64 inches at the shoulders, 60 inches at the hips, and 61 inches at the feet. Those specs make it significantly more spacious than typical mummy bags, which often taper to around 55 inches at the hips. This extra room allows for natural movement, whether you’re sleeping on your side, stretching out, or even sitting up cross-legged. Fully zipped, the Boost narrows to 64 inches at the shoulders, 53 inches at the hips, and 52 inches at the feet, bringing it closer to a standard mummy fit while still feeling spacious.
The Boost’s 20-denier nylon shell and lining further enhance comfort with an incredibly soft feel. Additional comfort-focused details include a puffy draft collar, a draft tube along the zipper, and a cinchable hood, all of which kept me snug on the coldest nights in my cabin in El Chaltén. Pulling the hood tight and zipping the bag fully created a cozy cocoon, cementing the Boost’s position as one of the comfiest down models on the market.
Therm-a-Rest packed the Boost 650 with thoughtful details that set it apart from traditional mummy bags. Its unique, standout WarmZip system lets you adjust the width (and thus temperature), allowing for extra space on mild nights or a more snug, thermally efficient fit in colder conditions. Integrated armholes add another layer of versatility, letting you keep your hands free for reading, grabbing gear, or adjusting the WarmZip without fully unzipping the bag. While I didn’t use the armholes (and honestly found them a bit gimmicky), I can see how some campers might appreciate them. They also function as vents, though I preferred unzipping the main zipper on warm nights.
Other comfort-focused details include a cinchable hood, plush draft collar, and a draft tube along the zipper to help seal in warmth. The Boost 650 also comes with both a compression sack and a large storage sack, making it easy to pack for trips and store properly between adventures. The kitchen-sink approach adds weight, of course, but it should also make this sleeping bag attractive to comfort lovers and gear nerds alike.
The Boost holds up well to regular use, but it’s not the most rugged sleeping bag out there. Its 20-denier nylon shell was specifically chosen for softness over durability, and it lacks the reinforced face fabric found in burlier designs. This makes it less resistant to moisture, abrasion, and rough outdoor use—not the best choice for sleeping directly under the stars or in high-exposure environments. Compared to bags with Pertex Quantum shells (such as the Feathered Friends Swallow UL 20) the Boost will require a little extra care to keep it in good shape.
That said, after a full month of nightly use, I’ve noticed zero loose stitching or escaping down—a great sign of long-term durability. The YKK anti-snag zipper pulls are another standout, preventing snags and tears that are all too common in lightweight sleeping bags. (I once put a massive rip in a Mountain Hardwear bag by catching fabric in the zipper, so I appreciate the Boost’s thoughtful construction here.) While it’s not the most rugged bag, treat the Boost well and it should hold up for the long haul.
Keeping a sleeping bag dry is crucial for comfort, particularly with down insulation. The Therm-a-Rest Boost 650 thoughtfully addresses this concern with several practical features. Both its shell and liner are treated with a PFAS-free durable water repellent (DWR) finish, encouraging moisture to bead up and roll away before it penetrates the fabric. Additionally, the bag utilizes 650-fill hydrophobic down insulation, providing enhanced resistance against moisture should dampness seep in. These features offer helpful protection against occasional contact with damp tent walls or minor moisture exposure, but they aren't foolproof. In consistently wet conditions, it's best to use a waterproof stuff sack and ensure your sleeping bag remains safely inside your backpacking tent.
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Longevity
Choosing durable outdoor gear and keeping it in use for longer is one of the best ways to reduce environmental impact. Our proprietary longevity rating assesses factors like overall build quality, materials, fabric denier, component durability, and real-world performance. A green check indicates that we expect the product to be long-lasting relative to its peers, a yellow check mark indicates average longevity, and a red X indicates a product that may have a limited lifespan.
Responsible Down
The Responsible Down Standard (RDS), developed by Textile Exchange, is the leading certification for responsibly sourced down and uses third-party audits throughout the supply chain to verify animal welfare, responsible farming practices, and safe working conditions. Recycled down is another responsible choice that helps reduce demand for newly sourced down while keeping existing materials in circulation. A green check mark indicates a product uses responsibly sourced or recycled down, a yellow check mark indicates the brand sources responsible or recycled down for the majority of its products but does not specify it at the product level, and a red X indicates the product does not use responsibly sourced or recycled down.
PFAS-Free DWR
Durable water-repellent (DWR) finishes can contain PFAS (per- and polyfluoroalkyl substances). These highly persistent “forever chemicals” are used in outdoor gear for their strong resistance to water, oil, and heat, but are linked to environmental contamination and a range of health concerns. A green check mark indicates the product uses a PFAS-free DWR, while a red X means the DWR contains PFAS.
Recycled Materials
Recycled materials are prevalent in outdoor gear, with nylon, polyester, wool, and down among the most common, but the composition varies widely. A green check mark indicates the product is made with a substantial amount of recycled materials (100% recycled or the core fabric that makes up most of the product is recycled), a yellow check means it contains a moderate to small amount of recycled materials, while a red X means there are no recycled materials in the product.
Bluesign Approved
Bluesign Technologies, based in Switzerland, operates a third-party textile management system that ensures materials are manufactured to strict environmental, chemical, and worker safety standards. A green check mark indicates a product is either a Bluesign Product (contains at least 90% Bluesign-approved fabrics and 20-30% Bluesign-approved accessories) or features a significant amount of Bluesign-approved materials. A yellow check mark means it uses some Bluesign-approved materials but less than the aforementioned category, and a red X means there are no Bluesign-approved materials in the product.
Responsible Manufacturing
This criterion evaluates a brand’s commitment to fair wages, safe working conditions, and reducing environmental impact through certifications and programs like Fair Trade Certified, Fair Wear Foundation, Worldwide Responsible Accredited Production (WRAP), and the Fair Labor Association, while also recognizing brands that manufacture primarily in the U.S. or Europe under strict labor and environmental regulations. A green check mark indicates a brand meets our responsible manufacturing criteria, while a red X means it does not.
Recycled and/or Reduced Packaging
Packaging can add significant waste to outdoor gear purchases, so many brands work to reduce its impact by using recycled materials, incorporating Forest Stewardship Council-certified paper products, and minimizing plastic and paper use. A green check mark indicates a brand uses recycled or reduced materials across all of its packaging, a yellow check indicates moderate or limited use of recycled or reduced packaging, and a red X indicates the brand does not make either of these efforts.
Repair Services
Repair services extend the lifespan of outdoor gear and reduce overall consumption, though programs vary widely. Some brands offer comprehensive repairs for a range of issues, while others provide limited or no repair support. A green check mark indicates a robust repair program, a yellow check mark indicates limited repair services, and a red X indicates the brand does not offer repair services.
Resale and/or Recycling Services
Resale and recycling programs help keep outdoor gear in circulation longer and out of landfills, ranging from trade-in resale platforms that offer store credit to take-back initiatives that recycle products at the end of their usable life. A green check mark indicates a brand offers both resale and recycling programs, a yellow check mark indicates it offers one or the two, and a red X indicates it offers neither.
Carbon Footprint Tracking
This criterion evaluates whether a brand measures, reports, and works to reduce its greenhouse gas emissions using established frameworks such as the Higg Index, Greenhouse Gas Protocol, or The Change Climate Project. A green check mark indicates a brand publicly reports greenhouse gas emissions data, sets clearly defined reduction targets, and uses established tracking frameworks such as Higg or The Change Climate Project. A yellow check mark indicates the brand tracks emissions and outlines reduction goals but provides limited data, lacks science-based verification, or does not clearly report progress. A red X indicates the brand does not appear to track greenhouse gas emissions or provides so little information that its efforts cannot be verified.
Annual Impact Report
Annual impact reports provide transparency and accountability by outlining a brand’s sustainability efforts across areas such as material sourcing, greenhouse gas emissions, waste, water use, supply chains, and packaging. A green check mark indicates a brand publishes a detailed, brand-specific impact report that closely aligns with our sustainability criteria and leaves little room for ambiguity. A yellow check indicates a brand provides some relevant sustainability reporting but lacks detail in key areas or is covered only briefly within a parent company report. A red X indicates a brand does not regularly publish an impact report.
Given its semi-rectangular shape, the Boost 650 offers more room to move than most traditional backpacking sleeping bags. I tested the size regular (fits up to 6 feet tall), and Therm-a-Rest offers an impressive six inclusive size options: short, short wide, regular, regular wide, long, and long wide—a rare level of variety in the sleeping bag market. I almost went for the 3-ounce-lighter short version (fits up to 5-foot-6) since I’m just shy of that height, but having used "short" bags in the past, I’ve often felt maxed out in them. Plus, if you’re choosing to sleep in the Boost you’re not exactly scrapping to save every ounce.
With a 64-inch girth at the shoulders, 60 inches at the hips, and 61 at the feet, the Boost offers way more room to spread out than standard mummy bags, which typically narrow into the mid-50-inch range at the hips. With the WarmZip zipped up, the bag narrows to 53 in at the hips and 52 in at the feet, but still allows for side-sleeping, rolling over, and stretching out with ease.
Nemo Disco 15 ($300): Roomy Without the WarmZip
If the Boost’s vents and roomy dimensions appeal to you, consider the Disco. The Disco has a unique hourglass shape that’s wide at the shoulders (64 in.), narrows at the hips (58 in.), and opens up again at the knees (63 in.), making it ideal for side-sleepers. It also features two vents at the shoulders, but they don’t open up to the inside of the bag; a thin scrim of fabric prevents passing your arms through and protects against drafts. Still, they’re another form of temp regulation, although the Disco lacks the Boost’s shape-changing central zipper, which is the true key to boosting warmth in such a roomy bag. All told, the Disco (which checks in with a similar 650-fill down and a 2 lb. 11 oz. weight) doesn’t have the impressive temperature range as the Boost but is still a comfortable alternative that costs $40 less. You can read our review of the Nemo Disco 30 here.
Therm-a-Rest Parsec 20 ($470): Comfort, Meet Minimalism
If you're loyal to Therm-a-Rest but are focused on shaving weight and bulk from your pack, the Parsec 20 makes a compelling case. At $470, it’s lighter and more compressible thanks to loftier 900-fill hydrophobic down insulation and a slimmer profile. And though shaped like a traditional mummy bag, the Parsec still remains roomier than most in its weight class. However, choosing the Parsec means sacrificing much of the temperature regulation and versatility you get with the Boost—not to mention spending an extra $130. Ultimately, the Parsec is ideal for ounce-conscious backpackers, while the Boost provides better value and more comfort-focused features for less.
Big Agnes Lost Ranger 3N1 15 ($400): Modular Versatility
For even more customization than the Boost, the Big Agnes Lost Ranger 3N1 gives campers three different sleeping configurations. You can use just the inner mummy-style bag, which is rated to 40 degrees Fahrenheit, opt for the outer quilt (a rectangular, hoodless design) rated to 50 degrees Fahrenheit, or combine them to create a down-filled hybrid bag rated to 15 degrees Fahrenheit. At 2 pounds 12 ounces, the Lost Ranger is a great option for those who frequently camp in warm environments—think the American Southeast or desert regions—but occasionally need a bag with true three-season warmth. While it’s a bit fussier to configure than the Boost, its modular versatility makes it a solid value despite costing $60 more.
The versatile, uniquely designed Boost is geared toward comfort-minded backpackers who want a bag they can also use for car camping, travel, or the occasional house guest. It’s heavy for hiking far, though, and a bit expensive for its weight and bulk.
Warmth / Weight
Comfort
Features
Durability
Water Resistance
Sustainability
With an hourglass shape that provides plenty of room at the shoulders and knees, the Disco’s dimensions are a boon for side-sleepers. Ultra-soft materials and zippered vents add to the comfort-first design—at the expense of some extra weight.
Warmth / Weight
Comfort
Features
Durability
Water Resistance
Sustainability
A three-season bag that undercuts much of the competition on price, the Parsec offers a competitive warmth-to-weight ratio, above-average durability, and a handful of thoughtful quality-of-life features. Roomy dimensions and the lack of a short size make it a less ideal fit for smaller users.
Warmth / Weight
Comfort
Features
Durability
Water Resistance
Sustainability
The Therm-a-Rest Boost 650 20 is an excellent sleeping bag for campers, travelers, and casual backpackers who prioritize comfort and versatility over shaving ounces. Its roomy semi-rectangular design, WarmZip adjustability, and ultra-soft materials make it a great option for sleepers who toss and turn or want a bag that adapts to changing temperatures. If you primarily car camp, sleep in cabins, or take relaxed backpacking trips with a larger pack, the Boost’s spacious dimensions and customizable warmth will be a huge plus. All told, those features have won us over as devoted fans. However, this bag’s bulky packed size and heavy weight make it less than ideal for weight-conscious backpackers or thru-hikers who need every inch of pack space.
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