One of my new favorite card patterns is a Screen card.
I showed this idea and my take on a three panel screen card at my Hartford Stamp Club. They loved it.
It fits perfectly into a regular size A2 Envelope.
The dimensions for this 3 Panel card are:
Main card is 8 1/4″ X 5 1/2″
Score at 2 3/4″ X 5 1/2″
another look to the side:
Here are the supplies I used: