SaFlips are made of mylar, which is generally harmless to coin surfaces. It is, however, hard enough to leave rub marks if not handled carefully. SaTFlips don't show up in a Google search, or my internal database, so please tell us where we can get information about them in order to answer your question.
I am going to say saflips just because I have used them.Plus the other one sounds like a cheap knowoff.
They are both about the same. But I would not recommend either of them, or any flip, for UNC or expensive coins.
I haven't heard of SaTFlips but I do use SAFLIPs. What are called Mylar flips are not really Mylar. Mylar is not a material but the original product name that was given to the material known as Polyethylene Terephthalate. Mylar is easier to say so it stuck. There is also a heat-sealer you can use on these flips that costs about $60 and seems to never wear out. I've been using mine now since 1997.
For what its worth, here are my thoughts on Flips: 1. Like GD, I would not recommend flips for uncirculated, proof, or expensive coins. The risk of damaging the coin is very high. Use other holders such as Kointains, Intercept Shield, Whitman, etc. 2. The only exceptions to (1) for me are for cheap circulated coins, or coins submitted for grading. When submitting coins for grading, I use the large 2.5" x 2.5" SaFlips, as the risk of damaging the coins (especially half dollars and silver dollars) from placing the coin in the flip is minimized. 3. Never, ever, EVER, used the soft flips, not even on a temporary basis!!! They contain PVC, and will damage your coins. They will eat copper coins, leave green spots on unc. silver coins, and haze proof coins. There have been numerous cases of coins which were submitted in soft flips to PCGS/NGC which later hazed in the holder, significantly reducing the value of the coin. If a coin is stored in a soft flip for a long period of time, the damage is irreversable. If you have a coin in a soft flip, take it out ASAP and remove the PVC residue with a dip in Acetone. If the coin was not in the flip long, it should be OK. IMO, the sale of these soft flips should be banned!! 4. When removing a coin from a flip (i.e. you bought a coin and want to put it in a holder for long term storage such as as Kointain), cut off each side of the flip and pull the top piece off. This minimizes damage to the coin. If you try to "fish" the coin out of the flip (especially a SaFlip) you might scratch the coin. This could easily turn an MS 65 Franklin Half into an MS 63 Franklin Half. Trying to save the flip for re-use is just not worth it. Well, there you have it. If you take only one thing from this, remember NEVER, NEVER, EVER, use soft flips!!!!! Not Ever!!
