I was also curious about this so I tried milling some 1/4" foamboard to see how it would work. I was pretty happy with the results. I used a compression bit so that I wouldn't get tear out on either side.
Randy
View attachment 491711
Very cool -- this is very good to know...
I was also thinking of milling unfaced foam (like 2" foam board) -- bit like this but on smaller scale: