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Rab Mythic Ultra (20°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 — 303 g lighter than the Rab Mythic Ultra (20°F) (43% less weight). If grams matter to you, that is the one to beat.
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Spec Rab Mythic Ultra (20°F) Sea to Summit Spark SP I
Weight 700 g · 0.700 kg · 1.54 lb 397 g · 0.397 kg · 0.88 lb
Brand Rab Sea to Summit
Category Sleep System Sleep System
Rab Mythic Ultra (20°F)
700 g

Winter-capable sleeping bag at 24.7 oz (700g) with 900-fill hydrophobic down, ideal for 3-season to winter transition camping.

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Sea to Summit Spark SP I
397 g

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

Full details →

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Rab Mythic Ultra (20°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 303 g (43%) lighter than the Rab Mythic Ultra (20°F) (700 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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