Aggregate (composite)

A good compromise is chopped fiber, where the performance of filament or cloth is traded off in favor of more aggregate-like processing techniques.

The upper limit to particle size depends on the amount of flow required before the composite sets (the gravel in paving concrete can be fairly coarse, but fine sand must be used for tile mortar), whereas the lower limit is due to the thickness of matrix material at which its properties change (clay is not included in concrete because it would "absorb" the matrix, preventing a strong bond to other aggregate particles).

Unless some practical method is implemented to orient the particles in micro- or nano-composites, their small size and (usually) high strength relative to the particle-matrix bond allows any macroscopic object made from them to be treated as an aggregate composite in many respects.

While bulk synthesis of such nanoparticles as carbon nanotubes is currently too expensive for widespread use, some less extreme nanostructured materials can be synthesized by traditional methods, including electrospinning and spray pyrolysis.

Casting them in a polymer matrix yields syntactic foam, with extremely high compressive strength for its low density.

Usually these are ceramic materials whose crystalline structure is extremely directional, allowing it to be easily separated into flakes or fibers.

The nanotechnology touted by General Motors for automotive use is in the former category: a fine-grained clay with a laminar structure suspended in a thermoplastic olefin (a class which includes many common plastics like polyethylene and polypropylene).

The latter category includes fibrous asbestos composites (popular in the mid-20th century), often with matrix materials such as linoleum and Portland cement.

Special molecules (graft copolymers) include separate portions which are soluble in each phase, and so are only stable at the interface between them, in the manner of a detergent.