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Granite Gear says:
The eVent Sil Compression DrySack allows you to maximize space inside your pack by reducing the packed size of bulky items like sleeping bags and clothes. The waterproof 30D Sil-Nylon Cordura construction is an incredible balance of strength and weight and an integrated roll-top closure further ensures complete protection. The eVent Sil Compression DrySack has a space-saving shape that purposely takes best advantage of the inner dimensions of a backpack. Not intended for submersion.
Once you've sealed the roll-top closure, you can cinch down the drysack with ultra-lightweight LineLoc compression straps. An innovative eVent air-purging bottom allows excess air to escape without jeopardizing weather protection. All seams are taped with eVent to provide further confidence. Not intended for submersion.
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