LaurieK47 left a question on a post about Tyvek from 2007. She wanted to know how I got this effect.
It is a while since I've used Tyvek so I had to have a quick try to remind myself. I cut an A4 piece in to smaller pieces remember it shrinks so take this in to account. I put a piece in between a folded sheet of non-stick baking parchment that I bought in a pound shop. I heated the iron to in between medium and hot, trial and error because each iron will be different. Hover the iron over the Tyvek until it begins to shrink the amount you want.
I can't tell you how many pieces I've wasted until I got it right. This video from joggles.com may help. Good luck with your project for A level :-)