Crease the Square in Half and Diagonally
0:30
Start with a 15 cm square sheet, color side down. Fold it in half top to bottom, crease firmly, and open it back up. Flip the paper over to the color side, then fold corner to corner both ways to make an X of diagonal creases. You should end up with one valley crease across the middle and two mountain creases through the corners. Sharp creases here make the next collapse fall into place on its own.
Tip
Run a fingernail or bone folder along every crease. Loose creases at this stage are the number one reason the waterbomb collapse fights you in step two.






