The problem with the thinner plastics, used for templates, is that one mistake in cutting with a sharp blade and you have likely damaged your template. I find that using 3 to 4 mm plastic gives you a better edge to cut against and can be shaped with heavy kitchen shears. The heavier plastics are frequently semi-opaque but can still be seen through enough to get your template spot on. I have searched the internet and find the well know auction site to be a good resource, but you have to buy fairly large sheets and it is somewhat costly. However, I make a lot of templates and find it cost effective, less problematic and more precise.