Coroplast is a great material to work with. It comes in different colors, it's rigid, and it's smooth surface makes a great race track for Hot Wheel cars. I use the 4mm coroplast. It also comes in a larger 6mm size. That size refers to the size of the flute (the holes in the material) You can also get several different lengths. I've been using 18" pieces, but it also comes in larger sizes.
The Coro-Claw is one of the best ways to make quick straight cuts. It also allows you to score the material, cutting only one side so you can bend it. You can find the Coro-Claw on amazon.