I have bought heat resistant (I think it was called) template plastic from Joann's with coupon. I got it in the quilting area with the quilting tools. I used it for applique shapes that I cut out and turned the edges with starch and ironed down. The plastic did not shrink, but I did get the iron too hot, or held it too long on the plastic with fabric to dry the starch and it buckled or rippled slightly. I probably had steam too as I always have water in the iron. If you use the lower setting it probably wouldn't do that. I am just always in a hurry. You can get a sheet for a couple dollars with a coupon. Worth a try. That is what I am going to try when I make this one:
https://nightquilter.com/tag/modern-hexies-mini-quilt/
Also, years ago, I think it was Sewing with Nancy, but could have been Kaye Woods, or one of the others. She made a GFG, sewing the hexies together on the machine by zigzag.