REI Co-op Flash 45 vs Six Moon Designs Swift X

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

Six Moon Designs Swift X is the lighter option — 425 g lighter than the REI Co-op Flash 45 (36% less weight). If grams matter to you, that is the one to beat.

Spec	REI Co-op Flash 45	Six Moon Designs Swift X
Weight	1,190 g · 1.190 kg · 2.62 lb	765 g · 0.765 kg · 1.69 lb
Brand	REI Co-op	Six Moon Designs
Category	Backpack	Backpack

REI Co-op Flash 45

1,190 g

Lightweight 45L versatile backpacking pack.

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Six Moon Designs Swift X

765 g

Highly configurable 50L ultralight pack with removable stay, hip belt and vest harness options to dial in fit and weight.

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REI Co-op Flash 45 vs Six Moon Designs Swift X: which should you buy?

If saving weight is your priority, the Six Moon Designs Swift X wins — at 765 g it is 425 g (36%) lighter than the REI Co-op Flash 45 (1,190 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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