…is the preferred material for pipe work installation in the home. It has stood the test of time. It is robust, looks neat and is non ferrous (will not rust).
Threaded steel pipe, sometimes referred to as malleable iron, is also an excellent choice. It is commonly used in a commercial environment, or in an area that is more prone to damage. E.g. A copper gas pipe under a door step or on the route you use to take out your wheelie bin would soon get dented, clips damaged etc so a steel gas pipe would be more practical.
Galvanised pipes are available (coated in zinc so will not rust). Steel pipes are more robust than copper and can stand impacts without damage. They also hold very little scrap metal value and are difficult to remove, as there have been cases where exposed copper gas pipes on the exterior of the property have been stolen by scrap metal thieves.
In my opinion, the worst material available. Requires no skill to install and completely removes the professionalism out of the trade. It has not been around long enough to be put to the test, doesn’t look neat, can be damaged by rodents (mice can chew their way through it). And if you see the photo in the gallery of a damaged plastic pipe, a burst is probable. This was removed from a property in the Fradley area where scalding hot water was pouring from the ceiling when a heating pipe had burst!
Plastic is however, the preferred material for under floor heating, or if burying a pipe in a concrete floor as there are no joints in the floor, and the concrete or screed does not corrode plastic.