The "Carrier Board" is used as a backer board to carry the graphic and TRF foil (colorizing foil) through the heat & pressure "laminator". The purpose is to prevent the foils from wrinkling from happening. Without the use of a rigid board, the chance of getting a wrinkle is very high.
This thin .020" thick fiberglass boards are made out of a high temperature "FR-4" material. Size is 8" x 10" and easily cut with a paper cutter to smaller sizes that may be more appropriate to the more common sizes you use most.
Because there are two boards to a pack, you have one to cut up into smaller sizes leaving the other for your largest graphics.
$17.95 / 8"x10", .020" thick