What is a sandwich panel?

What is a sandwich panel? 

A sandwich panel is a product used to clad the walls and roofs of buildings. Each panel comprises a core of thermoinsulating material, skinned on both sides with sheet metal. Sandwich panels are not structural materials but curtain materials. The structural forces are carried by the steel framework or other carrier frame to which the sandwich panels are attached. The types of sandwich panel are generally grouped by the thermoinsulating material used as the core. Sandwich panels with cores of EPS (expanded polystyrene), mineral wool and polyurethane (PIR, or polyisocyanurate) are all readily available. The materials mainly vary in their thermal insulating performance, sound insulating performance, reaction to fire and weight.