1. Arrange the postcards on one end of a sheet of plastic. Sandwich the cards between the two sheets of plastic.
2. Use an awl to poke holes through all layers at the corners of each postcard. Secure a brad in each hole. (See image.)
3. Bind edges of plastic with duct tape. Cut 1/2 inch off the width of a length of tape in an accent color; bind edges of plastic.
4. Tape each 4x12-inch piece of wood lengthwise; tape the accent color at the edges.
5. Center the 18x4-inch piece of 1/4-inch-thick balsa wood on right side of plastic, aligning the edges. Use duct tape to bind wood to plastic for the bottom of the holder.
6. Fold up the layered plastic to create the front and back of the holder. At each side tape a 4x12-inch piece of 1/8-inch-thick balsa wood to the plastic front and back.
7. To make a closure strip, cut a 6-inch-long strip from one tape color. Cut two 6-inch-long strips from the accent color. Bind the edges of the first strip with the accent-color strips, overlapping the edges 1/2 inch and wrapping remaining tape to the back.
8. Tape one end of closure strip to the top edge of the back piece. Fold the opposite end over the lip of the front, adding a hook-and-loop fastener to hold it in place.