Whats it called - engraving plastic?

Trying to find the name of the sign making plastic that is a sandwich of two colours - you engrave through the top layer to show the bottom one?


Thanks

Not sure what it is called but I have purchsed some from these guys before... http://hindleys.com/index.php/perspe...ate-sheet.html

Thats the stuff :)


Many thanks

How about traffolyte?