A very tough plastic piping its much cheaper and easier and safer to install over copper pipe you simply crimp on a fitting
and it has all but totally taken over as the superior way to do plumbing for supplying water.
However like all new products we will have to wait and see if it truly is the miracle product they claim it is now a little over 5 years on the market.
Already some problems are developing because people go to use a torch to change a fitting on a piece of copper sticking out of a wall and not realize its attached to a piece of plastic PEX.
but that's the least of worries just look at the problems and lawsuits brought by home owners over Polybutylene Piping
Which worked for a while then failed. Plus the new crimp on and self gripping Gator fittings coming out for copper pipe as well.
All these products that have not been long term tested and all buried with in walls . Add in the new closed cell foam insulation's I see nothing but disaster coming down the road. Plus what about the chemical BPA which can leech off plastic they warn not to drink water out of a bottle exposed to sun and where running hot water thru plastic.
when the finger pointing starts.
Yes all this new technology is making it much easier and cheaper to construct but at what price ?
Well I guess we will be finding out 20 years from now when homes start catching fire from over heating wires in closed foam insulation and start self destructing and leaking because no one had the foresight to say hey wait a minute lets really make sure this stuff is not going to cause problems.