Needle felting

I am thinking about doing a needle felt project with 2 of my classes. Maybe something like a coin/cosmetic/glasses pouch and if it works out a little 3-D animal.
Does anyone have any suggestions for a cushion to place the wool on as it is being felted? Foam is what is suggested but I don't have enough foam for an entire class. I am thinking of several layers of cardboard duct taped together as the backing, I could put together enough of those for a class. Do you think this will work? Any better suggestions?
This will be with the classes I trust to work with sharp needles. But any suggestions are appreciated.
I'm about to take off for work where so can't discuss this further until I return.