Expanded polystyrene and extruded polystyrene foam (Styrofoam) came to be used more recently for the construction of the entire airframe. Depron (the type of foam used for meat trays) blends rigidity with flexibility, allowing aircraft to absorb the stress of flying. Expanded polypropylene (EPP) is an extremely resilient variety of foam, often used in basic trainers, which take considerable abuse from beginners. Foam is used either in an injection mold to make a molded airframe or is cut out of sheet to make a built up airframe similar to some wood airframes. Airplanes of foam construction are frequently referred to as "Foamies".
