A purlin (historically also known as purline, purloyne, purling or perling) is a longitudinal, horizontal, structural member in a roof. Traditional in a timber framing there are three basic types of purlin: purlin plate, principal purlin, and common purlin.Purlins can also be seen in steel frame construction. For protecting the Steel purlins from the environment they may be painted or greased.Usually, cold-formed steel is used to make the Steel purlins that are thin enough to put the screws through. Cold-formed steels are made either by rolling or pressing the thin sheets of steel into any desired shape. These are less expensive for the manufacturer than their hot-rolled steel counterpart and are also easier to work with. Although the cold-formed steels are stronger than the hot-formed steel, they are more probable to break while under pressure rather than bend.