I have a Case-It Metal Disc Storage File 280 and am curious what the backing material and type of plastic are used for the sleeves. I think that the sleeves are standard to most DJ style cases.
Write the company and ask. I did that just a few days ago, with a company that made disc envelopes out of vinyl. (gag) They wrote back, directed me to some of their line that was done with polypropylene, and non-woven polypropylene, which is really quite good (I now have sample in hand).
They want to sell their stuff, they’ll usually talk.