Its essentially a fairly stiff plastic pipe which can be joined together with special push on fittings. You cut it with a knife(or special tool), you don’t need solder or flame and anybody can work with it.
It comes from several manufacturers now and one tipp I will give, is to start with one brand and stick to it. The fittings may all be labelled 15mm but they don’t always play well together.
With the current cost of copper worldwide, the savings over copper pipe is enormous even with the extra cost of the push fit fittings, so don’t cheap out on the brand of plastic pipe. You will thank yourself later.
Some of the push fit fittings you can undo and most are re-useable with a special removal tool(great if you make a boo boo). They will also go straight onto copper pipe.
If you open one, you will find an ‘O’ ring and a steel ring with some vicious looking teeth. A word to the wise here, don’t be tempted to put your finger into a fitting. Most unpleasant.
The ‘O’ ring does all the sealing. The end of the pipe (with a metal insert) is pushed home past the ‘O’ ring to as far as it goes. This leaves the ‘O’ ring about ½” from the end. The ring of teeth is closer to the outside and its sole job is to bite into the pipe to stop the water pressure blowing the pipe out. A very simple design that works great.
Here are some pitfalls.
Its just plastic. It scratches easily and an ‘O’ ring wont seal on the pipe if it has a scratch, even a little one. So you must be very careful to keep the end of the pipe protected. To do this you can keep it taped up when poking it through floor spaces or wall cavities. Check each time you’re about to push on a fitting, that the pipe is clean and free from scratches or bits that could scratch the ‘O’ ring.
Using the fittings. You can buy a tool that cuts the pipe cleanly and squarely or you can use a sharp knife. Just be sure to make it a square cut. Loosen the locking nut half a turn(some fittings don’t have one, don’t worry about it) Insert the metal insert(don’t forget it or it could blow off) into the end of your pipe, then insert the pipe end as far as it will go into the fitting. Ensure is all the way in and the locking nut is tight(by hand) and the jobs done. Pressurise the system to check for leaks before you seal the fittings into a wall or floor. This is not always possible but highly recommended.
So there you are. Go forth and plumb.