Corrugated galvanised iron or steel, colloquially corrugated iron (near universal), wriggly tin (taken from UK military slang), pailing (in Caribbean English), corrugated sheet metal (in North America) and occasionally abbreviated CGI is a building material composed of sheets of hot-dip galvanised mild steel, cold-rolled to produce a linear ridged pattern in them. Although it is still popularly called "iron" in the UK, the material used is actually steel (which is iron alloyed with carbon for strength, commonly 0.3% carbon), and only the surviving vintage sheets may actually be made up of 100% iron. The corrugations increase the bending strength of the sheet in the direction perpendicular to the corrugations, but not parallel to them, because the steel must be stretched to bend perpendicular to the corrugations. Normally each sheet is manufactured longer in its strong direction. CGI is lightweight and easily transported. It was and still is widely used especially in rural and military buildings such as sheds and water tanks. Its unique properties were used in the development of countries such as Australia from the 1840s, and it is still helping developing countries today. Corrugated galvanised iron is also called corrugated steel sheet or corrugated steel metal. This is used as a roof of trench for soldiers in the military to protect them from enemy's fire attack. It can also be used as the roof of the commander's post. The phrase "Corrugated Steel Sheet" was used in the book, "Infantry Combat", therefore, we can assume that corrugated galvanised iron is used as corrugated steel sheet in the military. History Henry Robinson Palmer, architect and engineer to the London Dock Company, was granted a patent in 1829 for "indented or corrugated metallic sheets". It was originally made from wrought iron. 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. In Australia and New Zealand particularly it has become part of the cultural identity, and fashionable architectural use has become common. CGI is also widely used as building material in African slums and informal settlements. For roofing purposes, the sheets are laid somewhat like tiles, with a lateral