Is it actually possibly to have air flow AND be water proof?
I don't see why not. depends on how you define both. Air flow I define as meaning that the pack stays off the back, like my Deuter does. water proof I am looking for a good level of water resistance from even heavy rain. the only problem with my Deuter is that putting a cover on it, as well as being faffy, cuts down on the air flow system, by blocking partially the air flow into the space between the pack and my back. If the pack itself were made from a hi viz water resistant material, and the zips had covers for rain protection, it would still allow the air flow to function as it presently does, without the need for a cover.