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Sea to Summit Spark SP III vs Western Mountaineering Ultralite 20F Sleeping Bag

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

Sea to Summit Spark SP III is the lighter option — 113 g lighter than the Western Mountaineering Ultralite 20F Sleeping Bag (14% less weight). If grams matter to you, that is the one to beat.
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Spec Sea to Summit Spark SP III Western Mountaineering Ultralite 20F Sleeping Bag
Weight 709 g · 0.709 kg · 1.56 lb 822 g · 0.822 kg · 1.81 lb
Brand Sea to Summit Western Mountaineering
Category Sleep System Sleep System
Sea to Summit Spark SP III
709 g

850-fill down sleeping bag rated to 0°C / 32°F.

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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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Sea to Summit Spark SP III vs Western Mountaineering Ultralite 20F Sleeping Bag: which should you buy?

If saving weight is your priority, the Sea to Summit Spark SP III wins — at 709 g it is 113 g (14%) 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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