What are best coin flips for long term storage of coins, and where can they be purchased online?

Question

I have seen flips made of prolar polyester, mylar, and vinyl.

I have been told not to use vinyl. I have also seen online things called Sa flips, and also Saf T Flips, but no explanation as to what the difference is.

Answer 1

I can't speak to the chemistry of part of this, but I believe the grading services typically want you to send coins to them in mylar flips, and I have heard that these are better in terms of maintaining raw coins long term, but they are more expensive.  The issue with cardboard, I believe, has to do with the acid and bleach used to produce the cardboard for the holders.  You can also check with a professional coin dealer.