I recently went on a tubing trip in New Orleans (90%+ humidity). We tubed a river for about 5 hours, of which 3 were in the rain (the dry sack was almost permanently wet). The dry sack was also used as a flotation device (with my flashlight, matches, medical kit, phone, dry clothes, and paracord in it) as I threw it to someone who was struggling to swim. I rolled the top somewhere between 4-6 times during the trip. It kept everything COMPLETELY dry.
In fact, it performed so well that at the end of the trip I emptied all of my things out, filled it with air, and rolled the top over two times to close it. I then tied it to a rock and submerged it for about 10 minutes in about 5 feet of water. The seal DID NOT hold with two rolls of the top lip. I dried the inside and repeated the exercise with 4 rolls of the top and the seal held.
SUMMARY: To get a truly water tight seal, roll the top 4+ times and it will perform wonderfully.
I've used these dry bags on many backpacking trips for several years now (including a two year through-hike and a 520 mile through hike) and they've held up well. They're my go-to when weather or river crossings could be an issue (and even when it's not, they're light enough to use on minimalist treks). I've yet to have one leak on me ... even after having to patch one with seam-grip and k-tape (having beaten the heck out of it bushwhacking and camping in very rugged backcountry areas), it's still waterproof.
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Was this a gift?:
Bottom Line Yes, I would recommend this to a friend