I like foam. Flies stay put, and can't blow away when the box is opened. I can see each fly in the box clearly, by itself. I cut my own slots in ripple-foam boxes and space the slots based roughly on the size of flies I'm going to store in them. Prefer the magnetic closures, no latches/snaps to fuss with or break. And they float if dropped in the drink. They must fit in a shirt pocket (small/medium). I drill a hole on each side and run a piece of dacron though them so I can hang them from a necklace too. Each box filled by category: terrestrials/attractors/pmd's/caddis/certain river/etc. Mine happen to be Orvis. Not expensive either, much less than the popular pre-slotted foam boxes. For saltwater, I just use a slotted-foam Bugger Barn.