Abstract: A composite board having a top surface, a core, and a bottom surface includes a polymeric material and a plurality of particles contacting the polymeric material to form a mixture. The weight percentage of the particles is greater than the weight percentage of the matrix material in the composite board. The volume of the plurality of particles range from 25% by volume to 88% by volume of the composite board. The composite board has a density in the range from 0.38 g/cm3 to 2.2 g/cm3. The top surface, the core, and the bottom surface are substantially comprised of the mixture.

Abstract: New composite materials having a high density of small particles, such as hollow microspheres, in a matrix material are disclosed. The microspheres are densely packed in the matrix material such that adjacent microspheres are positioned in contact with each other or very close together. Fiber flanking may be provided on the opposite sides of a layer of a core of composite material having the small particles and matrix material. Also disclosed are methods of making and using the composite materials.