The flexural stiffness of any panel is proportional to the cube of its thickness when exposed to flexural load. The purpose of a light density core inside a composite laminate is therefore to increase it stiffness and reduce its deflection under load exposure.
Cellular foam is the most common form and is fabricated from a variety of resin polymers including ABS – PP – PE – PVC and urethane. Honeycomb core, the combination of treated cardboard, aluminium foil and thermoplastic thin sheets, is also available. Balsa wood is an end-grain core, and its advantages include a very high compression strength, thermal insulation and ablative fire resistance.
The main advantage of using two parallel composite skins separated by a light density core is the high stiffness to weight ratio. The faces act together to resist tensile and compression stresses, and the core will resist shear and stabilize the faces against buckling. The adhesive that bonds the faces to the core is of critical importance.