Most of the double pocket coin flips sold today are made of vinyl (polyvinyl chloride). These PVC flips are available in a soft or hard version and risk damage to coins.
The chemicals that can bleed out of the vinyl, including the hydrogen chloride gas that the vinyl emits, are corrosive to coins, causing sticky green slime, cloudy appearance and microscopic pitting of the coin's surfaces. This is why museums don't use vinyl of any kind, because museums know that there is no such thing as safe vinyl.
SAFLIPS are made from polyethylene terephthalate, an inert and archival material ideal for preservation, long term storage, and a must for submissions to grading services such as PCGS. SAFLIP double pockets allow you to store a coin on one side and an insert note on the other side.
SAFLIPs are manufactured under rigorous conditions to keep them uncontaminated by oil or machine dirt. SAFLIPs are packaged in inert poly bags they are free of paper and cardboard dust that might cause spotting.
The SAFLIP story.....
In 1979 E&T Kointainer Co. began developing an inert, museum quality double pocket coin flip. Collectors would then have an alternative to the dangerous vinyl holders that were ruining so many coins. They invented a pure MYLAR holder, the SAFLIP copyrighted in 1980. Later, SAFLIP was improved to make it easier to fold and to make it airtight if a collector welded the flip pocket shut with a heat sealer. Acid and sulfur free identification cards that could be inserted in one of the pockets were also provided.
Since 1980, millions of SAFLIPs have been purchased and used by collectors, dealers and museums to safely store coins. SAFLIPs have been purchased by Harvard, Princeton, and Cornell Universities, and the James Madison University and the University of Michigan for use in their libraries and museums. The American Numismatic Association selected a SAFLIP for their authentication service in 1987. Recommended by Glenbow Museum.