you really need 100% cotton or other natural fiber for the colors to saturate the fibers & remain- on a polyester blend the colors will wash out- so it will only work if making wall hangings or something that will never be washed.
we generally press *cotton* fabrics to freezer paper for stability- I use painters tape around the edges- then when the kids are done with their master pieces I use a brown paper sack or plain newsprint paper as a press cloth- the paper absorbs the wax and sets the colors.