I just ordered 12 pieces from Walmart for under $11. They are 12x12x1/2 thick. Of course the 12x12 has a really wavy edge. Still I can manage 4 clear target dots at 6-8 meters or one centered dot at 8-15 meters.
Tired of hitting previous holes in 8 layers of cardboard and driving through to knock the cones off my darts.
These will do for now. Perhaps set 24' tall by 36' wide as a backstop and 12 tall x 24 wide x 1.5" thick as actual target foam leaving the total target 2" thick.
Maybe glue it to a plywood backing from the start. It is only $11 total if I glue it to cardboard as I can find rubber cement at home.