Thermarest Boost 650 20F/-6C

Comfort in the backcountry isn’t one-size-fits-all, and the Boost 650 is designed to flex with your adventure. Whether you're a side sleeper, a sprawler, or a midnight shuffler, this spacious semi-rectangular sleeping bag gives you the freedom to move and the space to actually sleep in the wild.

But here’s the genius: more space usually means more cold air to heat up. Not with the WarmZip system. Zip it up, and your roomy bag transforms into a snug, heat-trapping mummy-style cocoon - locking in warmth and boosting the temp rating by up to 10°F (6°C). It’s like packing two bags in one.

The Boost 650 is more than just a sleeping bag - it's your camp hangout zone. Built-in armholes let you read, cook, or sip that trail whiskey without peeling back the warm layers. Need to cool off? Vent with precision using the dual side zips or free your arms for airflow, without losing that core warmth.

And because every ounce matters, this bag is purpose-built for the backcountry. Lightweight. Packable. High-performance. Zoned 650-fill hydrophobic down puts insulation where you need it most—your core and upper body—cutting weight without cutting warmth. The shell and liner? Featherlight, soft, and made from 100% recycled nylon with a PFAS-free water-repellent finish that holds strong, even when the weather turns.

With thoughtful features like snag-free zippers, a draft-blocking collar and hood, and the flexibility to match your sleep style, the Boost 650 is ready to go wherever you do, whether that’s deep into the backcountry or just out under the stars.

Features

• Customizable Comfort: Enjoy the spacious freedom of the semi-rectangular bag or the cosy warmth of a mummy bag—pick the shape and temperature that keeps you comfy at night with just a zip.
  
• WarmZip™ Tech: Patent-pending centre zipper design zips up to reduce the bag’s internal space and tuck insulation around the sleeper to boost warmth by up to 10F/6C.
  
• Multi-Use Arm Holes: Reach the WarmZip, read a book, play cards or simply ventilate—do it all while tucked into your sleeping bag for elevated livability.
  
• Plush & Puffy: 650-fill, RDS-certified hydrophobic down is allocated to key areas with Zoned Insulation for refined heat efficiency and maximum cosiness.
  
• Eco-Conscious Materials: Shell and liner are made of GRS-certified, 100% recycled, soft-to-the-touch nylon and coated with PFAS-free water repellent.
  Inclusive Sizing: Each length—Short, Regular, Long—is also available in a Wide width, so you get the bag you want in the fit you need.
  
• Additional Features: YKK anti-snag zippers, cinchable hood, zipper draft tube, puffed draft collar, and a two-way entry zipper.
• Compression sack.
• Storage Bag.

Relevant Article

A Guide to Down Sleeping Bags

Specification

• Weight: Short: 1.02kg / Regular: 1.21kg / Long: 1.40kg
• EN Temp Comfort: 0C
• EN Temp Limit: -6C
• EN Temp Extreme: -23C
• User Height: Short: 168cm / Regular: 203cm / Long: 198cm
• Bag Length: Short: 188cm / Regular: 203cm / Long: 216cm
• Shoulder Width: 160cm / Regular: 163cm / Long: 165cm
• Hip Width: Width: 150cm / Regular: 152cm / Long: 155cm
• Footbox Width: Width: 155cm / Regular: 155cm / Long: 155cm
• Pack Dimensions: 24x17cm / Regular: 25x17cm / Long: 33x19cm
• Fill Materials: 650-Fill Duck PFAS-Free Hydrophobic Down, RDS
• Shell Fabric: 20D 100% Recycled Nylon Rip Stop
• Lining Fabric: 20D 100% Recycled Nylon Rip Stop
• Zip Side: Left