Trace and cut out a piece of foam (I used 2" thick), using the seat as a guide.
Cut out a piece of quilt batting and your material about 2" larger than the foam.
Lay down the layers in this order: material (right side down), batting, foam, board.
Pull the fabric over the edges and staple onto the board. Try not to get wrinkles around the corners when you gather them. (A little tricky but not too hard.)
One down, three more to go!
*All of the materials needed to do this can be found at any fabric store.