mark5.56,
The 'back' is slick/smooth like the other exterior you can see. The little credit-card sized flap tucks into a pocket on the outside, like those shark-flap wallets. (you can barely see the trim on the pocket seam on the outermost edges of the closed pouches in the pic). Very secure, very quiet.
The piece of paper partially exposed is showing the double-purpose pocket and divider between the two sets of 10-rounds. Perfect for a data card, ID info, copy of your NFA paperwork...
The rounds are held securely by the black elastic/stretchy nylon webbing loops.
The main panels have a plastic sheet sealed inside for rigidity and protection.
Attachment loop sewn on for ease of retrieving from a tight spot in your pack, and/or attaching some 550-cord retention lanyard...
I'm not sure of the dimensions when folded up, but it was slim. Rounds are well protected. Put your empties back in the same spots; no rattling around. Again, it's quiet...
I keep 20-rounds of match ammo in mine. Fits anywhere in my pack.