Step 1
Place a flat sheet of corrugated cardboard between two points.
For example, between the arms of a chair. Now push down and see how easily it bends.

Step 2
Fold the sheet as shown and using tape or string fasten the
open end of the vee so it won't slip and go flat when you press on it.
An easy way to do this is to make slits in the cardboard and with
2 knots in a piece of string, slit the string into the slit so the knots
stop on the outside of the cardboard slit.

Step 3
Now push down and feel the strength a fold can make!