What you are talking about are called "2x2s", because of their size. They have a mylar lining which completely covers the coin. Most are sealed by stapling, but there are also self-gluing types which many collectors avoid because of the possible ill effects of outgassing of the glue. With the relatively rare exception of iron or steel coins, rust is not a potential problem for coin storage, but since the 2x2s are neither airtight nor water tight, they cannot protect those coins. Neither a thin layer of mylar, nor Lightweight cardboard can protect a coin from physical damage, but with one possible exception 2x2s can't cause damage either. The exception is that failure to clinch the staples flat can cause damage to adjacent coins, and careless removal of staples when opening the 2x2s can result in scrapes or scratches. In several decades of collecting, your initial post was the first time I ever saw or heard the term "carded protectors"!
'Carded' coins is the way that 2X2's are described on eBay. Love the terminology. Perhaps one of those cards is a Mickey Mantle.
