During launch, an external fuel tank is positioned between the two solid rocket boosters. Although the boosters are recovered and reused after liftoff, the external tank (which has been sprayed with foam insulation) is neither recovered nor reused. Instead, it is jettisoned into a remote area of the ocean where it breaks apart.
Before it was used on any of the shuttles, the external tank insulation was tested in-flight on an F-15B.
It is insulation of that type which broke loose from the external fuel tank and impacted Columbia’s left wing eighty seconds after liftoff on January 16, 2003.