A clothes iron also flatiron or smoothing iron is a small appliance that, when heated, is used to press clothes to remove creases and help prevent the spread of infectious disease. It is named for the metal iron of which the device was historically made, and the use of it is generally called ironing. Ironing works by loosening the ties between the long chains of molecules that exist in polymer fiber materials. With the heat and the weight of the ironing plate, the fibers are stretched and the fabric maintains its new shape when cool.
The heft of a sad iron would proportionally effect the amount of heat held in the iron, and consequently how well the fabric would be pressed flat. The base of a sad iron is triangular shaped with a pointed tip to make it is easy to iron around buttons. They were heated on an open fire or a stove, and their metal handles had to be gripped with a thick potholder, rag, or gloves while ironing.