Just been on a very long and wet Coast to Coast trek, got a few of these, various sizes, packed all my stuff in dry bags then packed them in my rucksack, not a drop of water got through, using more than one really helped organise my pack, there not just waterproof but air tight so you can squash your stuff, roll down the top to seal and it stays compressed so saves space too, Truly Excellent! and forgot to say they work the other way round as well! I had a separate bag for wet and stinking socks kept all the water and stink in keeping everything else fresh and dry A MUST HAVE for walking in this country!