Therm-a-Rest Hyperion 20.
Nikwax Hydrophobic Down in a 1 lb 5 oz mummy bag rated to 20°F. The ultralight pick for backpackers who want a bag, not a quilt.
The Verdict.
Gavler Meta-Score
“The lightest 20°F mummy bag in production. Nikwax Hydrophobic Down provides genuine moisture insurance. Right pick for UL backpackers who want a traditional bag shape at quilt-competitive weights.”
The Gavler Verdict
Precision Engineering
1 lb 5 oz
Lightest 20°F mummy bag in production — quilt-competitive weight.
Nikwax Hydrophobic Down
Permanent DWR treatment on individual clusters retains 90%+ loft when damp.
ThermaCapture Lining
Reflective interior lining adds warmth without insulation weight.
Technical Specifications
The Scoreboard
Best-in-class for mummy-bag loyalists. Snug fit limits the appeal for side-sleepers.
Cast Your Vote
Do you think Therm-a-Rest Hyperion 20 deserves the #8 spot in Best Backpacking Sleeping Bags?
Best Price Availability.
Prices checked April 2026
Global Critique
“Lightest credible 20°F mummy bag on the market. The Nikwax treatment is the real deal.”
“The mummy bag for ultralight backpackers who haven't converted to quilts.”
“ThermaCapture lining adds perceptible warmth without weight — a genuine engineering advantage.”
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