This is a very lightweight, but stiff card, made from coated stock and lends itself to being used for loading blanks.
Available in the following sizes;
6ga, 7ga, 8ga, 9ga, 10ga, 11ga, 12ga, 13ga, 14ga, 15ga, 16ga, 17ga, 18ga, 19ga, 20ga, 24ga, 28ga, .410, .450