Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A sandwich structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff skins to a lightweight but thick core. The core material is normally low strength material, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density. Diagram of an assembled composite sandwich (A), and its constituent face sheets or skins (B) and honeycomb core (C) (alternately: foam core) Open and closed cell structured foam, balsa wood and syntactic foam, and honeycomb are commonly used core materials. Glass or carbon fiber reinforced laminates are widely used as skin materials. Sheet metal is also used as skin materials in some cases. The 1940 de Havilland Mosquito was built with sandwich composites, the balsa-wood core had on both sides plywood as the skin.