plastic flip corrosive or not?
 

I read somewhere plastic flips if vinyl, can deteriorate into green goo. But if they're mylar, or something like that, they dont.

I have bought a lot of coins here and there which came in flips with cards saying what they were. Numismatic items. Should I take them all out of the flips and put them in 2x2s or can I store them in the flips or what? This would be a huge pain in the ass because I have developed a fantastic collection of foreign silvers numbering in the hundreds and a few of these were valuable enough to worry about.

How can you tell from a flip whether its vinyl or not?

Please advise and correct any mistaken premises if any.

Re: plastic flip corrosive or not?
 

If you can get the plastic in the flap to crack by bending and folding it, it should be OK. If it is so soft that you can bend it without any damage it is PVC and should be avoided.
This is from memory and I don't know where I got it from. Thus, it could be wrong.

Re: plastic flip corrosive or not?
 

Look for vinyl flips on ebay. They are safe for long term storage. Search in the coin section. Less than 10 cents each with shipping. Less, if you email quality sellers to decrease shipping and ask for a volume discount. 5 cents delivered would be a good price. Smart sellers will make sure they state "PVC free". Buy some and compare your old flips with these. If your old ones have similar properties, "risking" it may not be a big issue for coins with little numis value. Maybe ask the guy you bought the coins from. Personally, if I really liked my collection that numbers in the 100's, I'd swap them out because of the volume discount. Sell some of the fugly coins and deliver in the old flips.