REGULAR Postcard 'L' Sleeve.
3-3/4 x 5-5/8".
4 mil POLYESTER (Mylar).
Sealed on 2 adjacent sides.

The polyester (archival) L-Sleeve is the best sleeve I have found for antique postcards and old photos for its archival properties. They are more expensive than the cheaper, more commonly used polyethylene sleeves so I use them only for my better postcards. These polyester sleeves are also the clearest sleeves I have found and they tend to stay clear unlike the polyethylene sleeves which become a little cloudy over time from rubbing against one another in my storage boxes. The L-Sleeve design also makes it very easy to insert and remove cards or photos without damage to the fragile ones. The polyester sleeves, to my knowledge, replace the mylar sleeves that used to be available (no longer) from another source.