I use the Sea To Summit dry bags with e-vent technology. The design is such that when you roll it shut and it waterproof to the outside elements, you can squeeze the bag so all the air goes out of it and it creates a vacuum seal around the clothes/items.
Great bag.
I use Alosak too but have had them open when jostled around my backpack. I switched to a smaller Sea To Summit dry bag size, (8 liter)in my backpack for when a rain hits unexpectedly. When not in use it rolls up to about the size of a skinny doughnut.
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