Tegris is a polypropylene composite that's being used for splitters and also used in the cage structure.
Tegris is used on the side of the cage. About 10 to 15 layers are compressed to form a composite 1/10 of an inch in thickness. It covers the outside surface of the door bars. It seems as if it would be easy to add to and existing cage if you're using NASCAR door bars.
Here's a good place to start your investigation.
Richard Newton
The Complete Trailer Handbook