Osprey Sirrus 36 vs REI Co-op Flash 45

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

REI Co-op Flash 45 is the lighter option — 30 g lighter than the Osprey Sirrus 36 (2% less weight). If grams matter to you, that is the one to beat.

Spec	Osprey Sirrus 36	REI Co-op Flash 45
Weight	1,220 g · 1.220 kg · 2.69 lb	1,190 g · 1.190 kg · 2.62 lb
Brand	Osprey	REI Co-op
Category	Backpack	Backpack

Osprey Sirrus 36

1,220 g

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

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REI Co-op Flash 45

1,190 g

Lightweight 45L versatile backpacking pack.

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Osprey Sirrus 36 vs REI Co-op Flash 45: which should you buy?

If saving weight is your priority, the REI Co-op Flash 45 wins — at 1,190 g it is 30 g (2%) 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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