Sturdy, raw, kraft chipboard. Not super heavy like bookboard: you could cut them with scissors with strong hands. You could use a (sharp) hole punch to add hole(s) for hanging or for binding like an accordion book. Acid-free, lignin-free, buffered and archival quality.
Shown in the additional photos with me holding against a Small Paper Mache House (and both the box and the lid, so you could get 2 shadowbox ornaments from one box).
3-1/2" x 2-1/2" (so ATC size, too!)
Alpha Stamps exclusives!
Set of 3.
For more information see the blog.