The latest 10-packs of these boxes seem to have less strength than previous packs which I have used and filled. My latest files placed in them make the bottom sag and it feels likes the bottom may break open as I carried them to storage. This may be problematic if you plan to put books in your boxes.While the thickness of the cardboard seems thinner than my previous boxes they are still an easy box to assemble.I still recommend them but do consider what weight of material you will place in them.