The Waterbomb Base
The waterbomb base is a base used to create many inflating origami models such as the waterbomb or the inflatable bunny. It is relatively easy, and is almost an inverted square base.
Step 1: Start with a square sheet of origami paper color side up and valley fold in half along the vertical axis
Step 2: Unfold and valley fold the paper across the horizontal axis
Step 3: Unfold and MOUNTAIN fold (opposite of the valley fold) the left corner around the back to touch the bottom left as shown below
Step 4: Unfold and MOUNTAIN fold the top right corner down to the bottom left
Step 5: Unfold
Step 6: Take a finger and place it under the center point and push up. This pulls the edges together. This is almost exactly the same as with the square base.
Step 7: Flatten and you have a completed waterbomb base! You now have what you need to make any models that require a waterbomb base to be folded first.