Paper Envelopes or Paper Flips of various sizes (usually 2 x 2) are still used for single coins. Be sure to use envelopes made explicitly for holding coins, otherwise your coins may change color (tone) over time due to reaction with sulfur or other chemicals present in the paper. Since the coin can not be seen, it is now out of favor with collectors.
Folders and Albums are sold primarily for series and type sets. Properly used, they offer moderate protection from wear and handling. Over the years coins may tone due to reaction with sulfur or other chemicals present in the folders and albums, and are therefore not a good choice for long term storage of higher grade coins. The coins are still exposed to light, air, chemicals and human touching. Albums have clear plastic covers over the coins, which slide in and out. This sliding action can leave unwanted and unattractive marks on the coin.