Duplexing allows us to glue cards together to make a much thicker product. We can Duplex up to 5 sheets together to either make a very thick card or to create a unique pattern along the edge of the card.
This works well when dealing with Digital, Lithography and Thermography where we are limited to a certain thickness of card to print on. Duplexing allows to have a lithography printed card at a much higher weight.