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Marmot Plasma 15°F vs Sea to Summit Spark SP I

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

Sea to Summit Spark SP I is the lighter option — 453 g lighter than the Marmot Plasma 15°F (53% less weight). If grams matter to you, that is the one to beat.
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Spec Marmot Plasma 15°F Sea to Summit Spark SP I
Weight 850 g · 0.850 kg · 1.87 lb 397 g · 0.397 kg · 0.88 lb
Brand Marmot Sea to Summit
Category Sleep System Sleep System
Marmot Plasma 15°F
850 g

800-fill down sleeping bag rated to 15°F (-9°C).

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Sea to Summit Spark SP I
397 g

Ultralight 850-fill down sleeping bag rated to 25°C.

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Marmot Plasma 15°F vs Sea to Summit Spark SP I: which should you buy?

If saving weight is your priority, the Sea to Summit Spark SP I wins — at 397 g it is 453 g (53%) lighter than the Marmot Plasma 15°F (850 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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