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Therm-a-Rest Vesper 20F vs Western Mountaineering Ultralite 20F Sleeping Bag

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

Therm-a-Rest Vesper 20F is the lighter option — 272 g lighter than the Western Mountaineering Ultralite 20F Sleeping Bag (33% less weight). If grams matter to you, that is the one to beat.
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Spec Therm-a-Rest Vesper 20F Western Mountaineering Ultralite 20F Sleeping Bag
Weight 550 g · 0.550 kg · 1.21 lb 822 g · 0.822 kg · 1.81 lb
Brand Therm-a-Rest Western Mountaineering
Category Sleep System Sleep System
Therm-a-Rest Vesper 20F
550 g

Ultralight quilt with 900-fill hydrophobic Nikwax Treated Down. Rated 20°F with neck baffle and footbox snap. Among lightest mainstream quilts.

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Western Mountaineering Ultralite 20F Sleeping Bag
822 g

Hand-sewn sleeping bag, 29oz, 850+ fill power goose down, three-season

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Therm-a-Rest Vesper 20F vs Western Mountaineering Ultralite 20F Sleeping Bag: which should you buy?

If saving weight is your priority, the Therm-a-Rest Vesper 20F wins — at 550 g it is 272 g (33%) lighter than the Western Mountaineering Ultralite 20F Sleeping Bag (822 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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