PPR is a polypropylene random copolymer pipe. They are suitable for cold and hot water pressurized plumbing and mechanical systems. It is usually joined by means of fusion welding,either as a end to end (butt) weld or a fusion weld into a fitting hub. There are mechanical slip fit fittings, but the big advantage is the economy and structural integrity of the fusion weld. This type of joining, if done correctly makes two pipes into one longer pipe.