Therm-a-Rest Boost 650 20F/-6C Sleeping Bag

Find your ideal balance of space and warmth. With a customizable shape, the Therm-a-Rest Boost 650 20F/-6C sleeping bag transforms from a roomy semirectangular bag to a thermally efficient mummy bag.

Temperature ratings are intended as a guideline to help you compare products, rather than a guarantee of warmth, since many different factors contribute to your comfort while you sleep. Backpacking bags are typically rated for temperature according to an independent testing protocol—currently International Organization for Standardization (ISO) 23537, though some older items followed European Norm (EN) 13537. Testing is based on a person wearing one base layer and a pair of socks, sleeping on an insulated surface with a minimum R-value of 5.38.

Each bag then gets 2 ratings: the Comfort rating is the lowest temperature at which the bag will keep the average "cold sleeper" comfortable, and the Lower Limit rating is the lowest temperature at which the bag will keep the average "warm sleeper" comfortable. Some brands determine their own temperature rating by aligning to the Comfort rating for women’s bags, to the Lower Limit rating for men’s bags, or somewhere in the middle for nongendered bags.

• The Boost 650 was built to backpack—with dialed-in materials and design to make it light, packable and high-performing in variable backcountry conditions
• As a spacious semirectangular sleeping bag, the Boost 650 provides all the room you need to side sleep, shift about, spread out and relax
• Zipping up the WarmZip center zipper transforms the shape of the Boost 650 from a semirectangular bag to a thermally efficient mummy bag
• WarmZip pulls the 650-fill-power down around your body and reduces the amount of space your body needs to heat, adding up to 10F (6C) to the Boost 650's temperature rating
• Shell and liner are made of GRS-certified 100% recycled nylon that was handpicked for its light weight and supersoft feel
• 650-fill-power RDS-certified hydrophobic down is allocated to key areas with Zoned Insulation for refined heat efficiency and maximum coziness
• Zoned Insulation places the down in key warmth-retention areas (on top, around your core and shoulders) and reduces it where it's less efficient (on the bottom)
• PFAS-free durable water repellent (DWR) coating and hydrophobic down keep the Boost warm and comfy even in wet weather
• Armholes let you reach the WarmZip, read a book, play cards or simply ventilate—do it all while tucked into your sleeping bag for elevated livability
• 2-way side zipper lets you ventilate around your torso or down by your feet
• Every zipper line on the Boost 650 has a durable YKK antisnag pull to eliminate annoying snags and damaging tears
• Standard Therm-a-Rest features like a puffy draft collar, a draft tube along the entry zipper line, and a cinchable hood round out the Boost 650's bliss-inducing comfort
• Inclusive sizing lets you get the bag you want in the fit you need
• Comes with compression sack and a storage sack