My theory is: if it can't leak out, it won't leak in. Whenever I buy dry bags and don't have a chance to use them in a rainstorm yet, I do a water test. That's filling the bag halfway with water, then checking the seams for leaks/condensation. I also flip them over after folding down the top and securing the clip. Then I lay the bag on dry paper towels with the seam side down on the paper towels. Then I leave the bag with water in it for a few hours. Excessive testing yes, but I don't want to take the chance of my sleeping clothes, cell phone, or food getting soaked. If you experienced this before you know what I'm talking about. Well, after testing each bag (I bought 2-30L, 2-15L, 2-10L, and one 20L), Caos nomad bags came though with flying colors...not one bag leaked...not one drop. Not even when I flipped them over filled with water. How is that for impressive. It has been my experience to press the air out of the bags before folding the top down and clipping it. I find my dry bags last longer this way. Closing the bag with air filled in it seems to stress the seams of the bags. We do a lot of camping and hiking and these dry bags will accompany us on every trip. Thank you to all the reviewers of this product who helped me make my decision to purchase.