Hi,
Coroplast is a corrugated plastic sheet -- often used for signs, and the bins that the Post Office uses. Very durable and resistance to many solvents. It is usually 4mm thick, and comes in about 8 or 12 colors.
The OP describes Gylon
here.
I would also mention Gorilla Tape -- black (somewhat shiny, with a light gray sticky face), very tough, and very sticky.