Duplexing, or the adhering of two papers together is a great technique. It is particularly useful in the following circumstances:
To prevent any letterpress printed impression show through on a two-sided letterpress printed piece.
To allow the card to have one paper color and/or texture on one side and a completely different paper color and/or texture on the other side.
To make a paper thicker than it is manufactured by the paper mill.
To make the final card thicker than can be printed on the offset presses.
Triplexing is the same as duplexing, except three sheets of paper are used. Sometimes there are three distinctly different paper colors used, and other times there are two of the same sheets of paper used for the top and the bottom sheets, with a second paper color placed in the center.
A liquid adhesive is used for duplexing. As the adhesive dries, it pulls the sheets of paper together and bind them permanently. Because of this pulling and binding action, it is not advised to duplex a card that has been embossed. The drying of the duplexing adhesive will pull the embossing down a little, and it will pull the paper on the opposite side down into the back of the embossing, causing a low spot on the non-embossed side of the card. Triplexing, with a more rigid paper in the center will help to minimize this artifact.
The most frequently produced items are duplexed wedding invitations, duplexed business cards, duplexed Mitzvah invitations, and duplexed stationery.