Balsa core

Balsa core in which the wood grain runs perpendicular to the panel faces, so loads are carried along the strong axis of the timber's cells. This orientation gives far higher compressive and shear properties than flat-grain timber and is the standard form of balsa for structural sandwich cores.

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.

A lightweight open-weave fabric used as a flexible carrier or stabiliser. In core materials it is bonded to one face of small core blocks so the sheet can drape over curved moulds, while in roofing membranes and coated fabrics a scrim acts as the reinforcing carrier that gives the sheet dimensional stability and tear resistance.

The mass per unit volume of a core material, used as the primary grade designation for structural foams and honeycombs. Higher densities generally bring higher strength and stiffness at the cost of weight, so cores are specified by density alongside thickness and cell or grain structure.

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.