Music Triangle Edunation The triangle is an idiophone type of musical instrument in the percussion family. It is a bar of metal, usually steel but sometimes other metals such as beryllium copper, bent into a triangle shape. The instrument is usually held by a loop of some form of thread or wire at the top curve The triangle is one of the most identifiable percussion instruments. Getting its name from the shape of the bent metal from which it's made, the triangle creates a bright metallic and shimmery sound.