Self-Closing Non-Modular Triangles: 20

Each box on this page has been folded from a single square or rectangular sheet of paper. Slightly stiffer paper, like TANT, will perform better than thin/soft paper.
 
The boxes at left are called Pop Sacks because a gentle squeeze makes them pop open. The Tetra Boxes at right, designed by Jane Rosemarin, can be hung on a holiday tree with small treats tucked inside them. They close by inserting a tab in a slot, while the Truncated Tetrahedral boxes shown below, designed by Arnold Tubis, are closed by overlapping three flaps.