I use 100% cotton for this technique. Sue is done with crayons on 100% cotton so you an see the effect. Polyester won't absorb the wax dye very well. Get a few samples of different material and do the trial error method till you find what you like. Course or smooth, saturated color or soft color. It is all up to you.
You have a great idea and just have to experiment to find the look you like.
peace