It probably doesn't. I had just heard it was a way
to tell if the PVC had some kind of metal particals,
or whatever. I'm not that much up on PVC, but the rumor
I had heard was the "grey" PVC was better for HF rf use
compared to the white stuff. But I don't really know.
I've tried both, and never had any problems. The loading
coil on my shorter mobile antenna is wound on grey PVC,
and so far, I've never noticed any adverse effects.
My 2nd antenna uses a thin plastic tube, about like what
you would see on a sidewalk blower, or whatever...
Never noticed any problems with it either. I seem to have
about the same performance as an open frame coil, as far
as I can tell, and I've never noticed any heating, or
melting, etc..
My comment was more to protect the microwave, rather
than endorse the value of PVC nuking...:/ I have
tried it though...The grey stuff does stay cold when
nuked...Whatever thats worth..I didn't try the white
though...I've never had trouble with any material as far
as end insulators...I've run legal limit through plastic
coathangar insulators 3 inches long, and didn't arc...
That I could tell anyway...Same for PVC or wood...
The only time I've ever arced, was when the bare wire was
actually rubbing a tree branch...I started to burn it
up...Probably had been that way 2 weeks before I noticed
it..
MK