In order to make some toys out of paper, such as paper ninja throwing stars or butterfly knives, you need very stiff paper so the toys hold their shape. While you can use card stock, it is also possible to make your own hardened paper from regular printer paper. This paper will be as stiff as card stock and less expensive. After hardening it, you can cut the paper or fold it as needed for projects.
Fold a sheet of blank printer paper in half from top to bottom. Crease the fold and unfold it.
Squeeze a liberal amount of white glue on one side of the open paper. Spread the glue into an even coat on that one side with a sponge brush. Leave about a quarter inch around the outside of the paper without glue.
Turn the paper so that the glued side is closest to you. Slowly fold the paper along the crease you made in Step 1. Press the sides together starting at the folded edge and smoothing it outward to avoid getting wrinkles and air bubbles between the sides.
Repeat Steps 1 through 3 with the same piece of paper. Now you have a small rectangle of glued paper that is a quarter of the size of the full sheet. Place the glued paper between two pieces of kitchen parchment paper, and place a heavy book on top for 24 hours until dry.
Cover your work space with a plastic dust sheet to prevent glue from sticking to the table. Do not use newspapers because they will get the paper that you are hardening dirty. Use glue that dries clear. If you do not have a sponge brush, make a glue spreader from a half sheet of paper rolled up. Squash the end into a spreading tool.