What is XLPE Insulation? What are its advantages compared to PVC?

http://kalingacable.com/gifs/xlpe-data.doc

http://www.nehacables.com/comparitive_properties.html

and many more if you google

Cross-linked polyethylene. I don't recall if its temperature rating is higher or lower than PVC. One or the other of these materials might withstand certain chemicals better.