Six sheets of 6 x 13 matboard. From the Sizzix Site: Custom-made double-sided mat board for Sizzix big and original dies. acid free. Compatible with the Sizzix BIGkick and Big Shot machines (not included). No ordinary Mat Board, Little Sizzles were made for the unique dimensions of Sizzix ScoreBoards XL dies. All Little Sizzles Mat Board are acid free. The thickness of each Mat Board sheet is approximately 0.047 inches