Core density

The lightweight central layer of a sandwich construction, bonded between two thin, stiff face sheets to raise a panel's bending stiffness with minimal added weight. Common structural cores include polymer foams, honeycombs, end-grain balsa and syntactic materials, each specified by density, thickness and shear properties.

The shear loading carried by the core of a sandwich panel as it bends, transferring load between the two face sheets. Core shear strength and shear modulus are primary selection properties for core materials, and core shear failure is a common design-limiting mode in sandwich structures.

A material's strength divided by its density, commonly called the strength-to-weight ratio. High specific strength is the principal reason fibre-reinforced composites displace metals in weight-critical aerospace, motorsport and marine structures.

Closed-cell polyvinyl chloride foam supplied in sheet form as a structural sandwich core. Crosslinked grades offer higher stiffness and temperature resistance, while linear grades are tougher and more ductile; both are widely used in boat hulls and decks, wind turbine blades and vehicle panels.