There are various pipes made of various materials in your home and dependant on the job it does determines the material its made from.
They can be:
Also a factor when choosing pipe is the diameter (or "bore" as its sometimes known).
Common sizes in your home are:
12mm (Chrome from pedestal tap feeding fire.)
15mm (Average size in most homes now.)
22mm (Average size in most homes now.)
28mm (Circs off some primatic cylinders.)