Corrugated galvanized iron (colloquially corrugated iron or pailing (in Caribbean English), commonly abbreviated CGI) is a building material composed of sheets of hot-dip galvanized mild steel, cold-rolled to produce a linear corrugated pattern in them. The corrugations increase the bending strength of the sheet in the direction perpendicular to the corrugations, but not parallel to them. 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 like Australia from the 1840s, and it is still helping developing countries today.

Corrugation today
Today the corrugation process is carried out using the process of “Roll Forming”. This modern process is highly automated to achieve high productivity and low costs associated with labour. In the corrugation process sheet metal is pulled off huge rolls and through rolling dies that form the corrugation. After the sheet metal passes through the rollers it is automatically sheared off at a desired length. The standard shape of corrugated material is the round wavy style, but can be easily modified to a variety of shapes and sizes by simply changing the dies [4].
Many materials today undergo the corrugation process. The most common materials are ferrous alloys but may also span to stainless steels. Copper and aluminium are also used. Regular ferrous alloys are the most common due to price and availability. Common sizes of corrugated material can range from a very thin 30 gauge (.012 inches = 0.305 mm) to a relatively thick 6 gauge (.1943 inches = 4.94 mm). Thicker or thinner gauges may also be produced.
Other materials such as plastic and fibreglass are also given the corrugated look. Many applications are available for these products including using them with metal sheets to allow light to penetrate below. However, these sheets are not formed through the corrugation process.

Pitch and depth

The corrugations are described in terms of pitch (the distance between two crests) and depth (the height from the top of a crest to the bottom of a trough). It is important for the pitch and depth to be quite uniform, in order for the sheets to be easily stackable for transport, and to overlap neatly when making a join. Pitches have ranged from 25 mm (1 inch) to 125 mm (5 inches). It was once common for CGI used for vertical walls to have a shorter pitch and depth than roofing CGI. This shorter pitched material was sometimes called “rippled” instead of “corrugated”. However nowadays, nearly all CGI produced has the same pitch of 3 inches (76 mm).