They are expensive! Go to the dollar store and buy yourself a sheet of foam core board. It is 20X30 inches.
Cut once horizontally and 5 times vertically. You can get 10 boards to wrap around for the $1.00-$1.50 that you will spend and they will last you forever. I have made enough of them to do a 10 ft wall of display of fabric 5 feet high. I purchase mine at Dollar Tree and it is in the area where poster board is sold. Save the big bucks for fabric purchases. Ann in TN