They are certainly very hard, perhaps ABS plastic. So far I've not had any issues, but I do try to put all of the chips into the PVC-free flips.

As with other "filing" systems, you either need to leave room for expansion, or you will be constantly shifting chips to make room for more. I have yet to find the ideal, but I don't think I'm wasting financial resources in that search. And I guess I neglected to mention two other storage methods that I use...

Square tubes - They hold 20 chips and I use them to hold my $1 traders, when I get a stack of 20.

Racks - They hold 100 chips (5 rows of 20) I use several to hold my "new, but not yet filed" chips and others for my traders, i.e., Atlantic City traders, Wet traders, $1 traders, Snapper traders, $5 traders, Foreign traders, and Yes, even PC traders!

Jim