Cross-Linked Polyolefin
Thomas & Betts CPO187-0-25 Heat Shrink Tubing ST Cross Linked Polyolefin Blac...
This ITE item comes with a clear list of specs and limitations.
3M Itcsn-1500-25'-Black-Reel Heat Shrink Tube, Heavy Wall, 3:1 I.D. Shrink
A nice touch is the matte black surface, which doesn't glare under bright lights.