Therm-a-Rest Boost 650 20F/-6C review

The Boost 650 answers a common complaint about mummy bags: they feel tight. It is a semi-rectangular bag with a second zipper, which Therm-a-Rest calls WarmZip, running down the center. Zip it up and the bag pulls the down closer around your body like a mummy, which the company says adds up to 10°F to the rating. EN ratings are 32°F comfort and 20°F limit. Arm holes let you read, eat or vent with your arms out, and a two-way YKK side zipper opens at the feet. The 650 fill hydrophobic down is zoned toward the top and core, and the shell and liner are recycled nylon with a PFAS-free DWR. The Regular weighs 2 lb 11 oz, and six sizes run from Short to Long Wide. The list price is $339.95 for the Regular, and it was on sale for $237.89 when we checked, which makes it a strong buy while the discount lasts.

Who it is for

campers who feel trapped in mummy bags

Price

$339.95 list for the Regular at the Therm-a-Rest store (Cascade Designs), on sale for $237.89 when checked.

Regular price $339.95 Sale price $237.89
Quoted from the vendor pricing page on November 12, 2026.

Key features

• WarmZip center zipper converts the bag to a mummy shape
• EN comfort 32°F and EN limit 20°F
• 650 fill hydrophobic down with zoned insulation
• Arm holes for reading or venting without unzipping
• Six sizes from Short to Long Wide

Strengths and weaknesses

• Strength: Therm-a-Rest says WarmZip adds up to 10°F to the rating
• Strength: Arm holes let you sit up in camp inside the bag
• Strength: Wide versions for broad-shouldered sleepers
• Weakness: 2 lb 11 oz Regular, heavier than mummy bags with the same rating
• Weakness: 32°F EN comfort is warmer than the Disco 15 or Parsec 20
• Weakness: List price of $339.95 if the sale ends

Key facts

• Price: $339.95 list (Regular), $237.89 on sale when checked
• EN comfort / limit: 32°F / 20°F
• Weight: 2 lb 11 oz (Regular)
• Insulation: 650 fill hydrophobic down
• Fits up to: 72 in (Regular)

Where it ranks

Therm-a-Rest Boost 650 20F/-6C is No. 5 in our Best Sleeping Bags verdict.