the toilet stall stuff is 10-15mm thick and usually faced both sides with formica or the like. core is dark red to brown. vandal proof, burn proof and easy to clean.

i believe in the states you would call it micarta, garolite or just paper phenolic. i have a small slab that is around 40mm thick and unfaced, most likely from some electrical installation.

corian might also make a good insulator but would be heavy.