Microsandwich Honeycombs
In new type of honeycomb panel called "microsandwich honeycomb," walls filled with solid plastic foam reinforced with microspheres. Have compressive and shear strengths 50 to 70 percent greater than those of conventional, unfilled honeycombs of comparable dimensions and densities. Foam and hollow microspheres add little to weight but increase strength substantially. Useful in aircraft, automotive, and marine structures in which high strength and low weight important.
Bhat, Balakrishna↗