eVent works well!
I have been using this bag for about a year now. I really like the eVent technology because it allows for air to escape out of the bag, but prevents water from getting in. I was skeptical that it would work, but with testing it work outstandingly well. I primarily use this bag for traveling because it is so light and packs down small with out the need for compression straps. It it if you are looking to save some weight and like eVent technology.