As srs77 mentioned, the inserts have the consistency of a semi pliable rubber. This link will show you how flexible the inserts are.
http://www.amosadvantage.com/scotto...Mov01545.mpgI have been a supporter of these holders in the past on this forum. I can't say that I would support the use of these anymore. The issue has to deal with the toning that I have been struggling with with the coins in these holders. I have PCGS and NGC slabbed coins right along side of these holders. The slabs are stored in a NGC slab box with sacrificial cents, the slab boxes go to to a Ziploc bag with a 40g canister of silica gel, all the air pushed out and sealed. Stored in a area with constant temperatures and still toning on the coins in the in
Coin World premier coin holders.
I have used trial and error to determine what the culprit is and I think it is the inserts. At this point I am going to use 2x2's and put them in the acrylic snap case that the inserts go in. I hope that will solve the issue.
Maybe others have had success, but with the 100 or so I have purchased over the last 2.5 years I have had toning issues. I purchased these from Amos Advantage (they have good customer service) and voiced my concerns about these holders. There seems to be something in the inserts that doesn't agree with some of the coins. I mainly have seen issues with modern proofs that are in these holders in my type set.