I don't really think its about floating or sinking. I don't care... The more important quality is a string or line that attaches the box to your vest. Yeah, I have boxes with and without strings, but I'll always remember my buddy's first trip to the San Quan, when, as he changed to his second midge, he fumbled and lost his box with over 300 newly tied "killer" flies. It floated like a cork for about 30 yards, before sinking in the fast current. As a result, my favorite "river" boxes are attached to my vest.

Just my 2 cents.