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Osprey Sirrus 36 vs Zpacks Arc Blast 55L

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

Zpacks Arc Blast 55L is the lighter option — 770 g lighter than the Osprey Sirrus 36 (63% less weight). If grams matter to you, that is the one to beat.
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Spec Osprey Sirrus 36 Zpacks Arc Blast 55L
Weight 1,220 g · 1.220 kg · 2.69 lb 450 g · 0.450 kg · 0.99 lb
Brand Osprey Zpacks
Category Backpack Backpack
Osprey Sirrus 36
1,220 g

Women's ventilated 36L pack with AirSpeed back panel.

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Zpacks Arc Blast 55L
450 g

Frameless Dyneema pack with excellent load carry for its weight.

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Osprey Sirrus 36 vs Zpacks Arc Blast 55L: which should you buy?

If saving weight is your priority, the Zpacks Arc Blast 55L wins — at 450 g it is 770 g (63%) lighter than the Osprey Sirrus 36 (1,220 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 backpack page, or browse the full gear weight database.

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