I use card stock. I used a lot when I was teaching and had some left over. Found templates for the size I wanted online and printed the hexies out on my printer. Had printing on one side so thus I recycled. I also have bought from paperpieces.com.
Here's one project, 2 inches on a side, my current one is much smaller hexies, 1/2 inch on a side.
http://www.quiltingboard.com/picture...t-t240892.html