Corrugated galvanised iron

Corrugated galvanised iron (CGI) or steel, colloquially corrugated iron (near universal), wriggly tin (taken from UK military slang), pailing (in Caribbean English), corrugated sheet metal (in North America), zinc (in Cyprus and Nigeria) or custom orb / corro sheet (Australia), is a building material composed of sheets of hot-dip galvanised mild steel, cold-rolled to produce a linear ridged pattern in them.

Henry Robinson Palmer, architect and engineer to the London Dock Company, was granted a patent in 1829 for "indented or corrugated metallic sheets".

It proved to be light, strong, corrosion-resistant, and easily transported, and particularly lent itself to prefabricated structures and improvisation by semi-skilled workers.

It soon became a common construction material in rural areas in the United States, Argentina, Spain, New Zealand and Australia and later India, and in Australia and Argentina also became (and remains) a common roofing material even in urban areas.

The most common materials for corrugated iron are ferrous alloys (e.g. stainless steels), aluminium and copper.

A design of corrugated galvanised steel sheets "Proster 21", used as formwork, has 21 millimetre deep V-shaped pits.

Although galvanising inhibits the corrosion of steel, rusting is inevitable, especially in marine areas–where the salt water encourages rust–and areas where the local rainfall is acidic.

Corroded corrugated steel roofs can nevertheless last for many years, particularly if the sheets are protected by a layer of paint.