This is the first step. I cut the handles and bottom off the plastic bag to make it a square.
I put the plastic rectangle between 2 sheets of regular paper. The iron was on a rayon/cotton setting. You just move it around, then flip it over and do the other side. Be sure to get the edges. I just did the small size because that was the size of my paper and I didn't want to mess up my iron. The tutorial says that 8 layers is the best. I haven't tried anything else to say.
After it cools, you can cut it to any size you need. You can sew it just like fabric- by hand or on a machine. I used it as a lining. It wasn't thick or rigid, but it works.