Take a raw egg (yellow or white as you like, provided it is raw and preferably fresh), set it exactly vertical on its major axis (you can use your GPS to determine perfect verticality), go up gently on the egg, it will not break, as long as you keep some balance.

Imagine a ZEPHYX windscreen, imagine the wind in Ushuaia, during a storm warning; it will be the same, it will not crack... And it always will be as effective, but still you should avoid climbing on it.