Sandwich structures, consisting of high density skins separated by a low density core, are predominantly used to produce low-weight, high stiffness panels such as automotive load floors or energy absorbing components for occupant and pedestrian safety.

By creating a sandwich structure with a core twice the thickness of the skin, panel stiffness may increase by a factor of seven whilst the weight increase could be as low as just 3%.

Sandwich structures have been produced from self-reinforced polypropylene skins with different core combinations, including 10mm expanded polypropylene foam, polypropylene honeycomb, paper honeycomb and polyurethane foam, using a hot-melt adhesive film.

Tests on 300x25mm beams sectioned from the panels showed that honeycomb panels are stiffer than foam panels due to the inherent shear stiffness of the honeycomb. Paper honeycomb panels are stiffer and less costly than polypropylene honeycomb panels.