Sandwich construction

A form of construction used for hulls,
decks and houses, in which two relatively dense skins are held apart and
stabilised by a thicker core of lightweight material. The core may be of balsa
wood, for example, or of foamed plastic. The idea is to save weight and achieve
stiffness, for although a thick skin of plastic material may be quite strong it
will bend easily. Two such skins held apart and prevented from buckling by an
inner core can be a hundred times stiffer than either alone. But it is
essential to get a good bond between skins and core, and to be sure that there
are no cavities into which water could penetrate.