This is the foambord I use for my sculptingstands. This can be baked with the sculpture in the oven. This will give you a smooth plain surface to sculpt on.
Kapa line Polyurethane White 701 2440x1220x10mm 12 pack
KAPA® Lightweight foamboards with a polyurethane foam core (PUR)
KAPA®-Mount - Fancy Papers
KAPA®-Line - Fancy Papers
Ideal for crafts, framing, mounting displays, exhibits, and school projects White foam board, lightweight but strong and rigid surface 3/16 thick
UCreate Foam Board, White, 22 x 28, 5 Sheets
UCreate Foam Board, White, 22 x 28, 5 Sheets : Office Products
Foamboard Kapa Line - Vunder
are lightweight laminated matt white panels. They are ideal as a base for screen printing, digital printing, brush and spray painting techniques
Kapa Line Boards
Foamboard Kapa Line - Vunder
KAPA® plast, Plastic coated foam board
UCreate Foam Board, White, 22 x 28, 5 Sheets : Office Products