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Therm-a-Rest Vesper 900 vs Zpacks Sleeping Bag 20°F

Weight and specs compared for 2026 — and which one to choose.

Zpacks Sleeping Bag 20°F is the lighter option — 153 g lighter than the Therm-a-Rest Vesper 900 (28% less weight). If grams matter to you, that is the one to beat.
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Spec Therm-a-Rest Vesper 900 Zpacks Sleeping Bag 20°F
Weight 550 g · 0.550 kg · 1.21 lb 397 g · 0.397 kg · 0.88 lb
Brand Therm-a-Rest Zpacks
Category Sleep System Sleep System
Therm-a-Rest Vesper 900
550 g

Ultralight sleeping bag with 900 fill-power hydrophobic goose down. 360g of down fill. Excellent warmth-to-weight ratio for three-season backpacking trips.

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Zpacks Sleeping Bag 20°F
397 g

Ultralight 900-fill down sleeping bag rated to 20°F.

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Therm-a-Rest Vesper 900 vs Zpacks Sleeping Bag 20°F: which should you buy?

If saving weight is your priority, the Zpacks Sleeping Bag 20°F wins — at 397 g it is 153 g (28%) lighter than the Therm-a-Rest Vesper 900 (550 g). That said, the heavier option may justify the extra grams with more capacity, durability or comfort, so weigh the trade-off against how you'll use it.

See where both rank against everything else in this category on the lightest sleep system page, or browse the full gear weight database.

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