The strength of a composite material will depend sensitively on that of the fibre chosen for reinforcement. Metallic and non-metallic whiskers can be very strong and other less strong, but more practical, fibres such as carbon, silica and boron are now available in experimental quantities. Some of the non-metallic whiskers, and the last three fibres mentioned, will no doubt eventually be made on a production scale.

The strongest drawn wires yet available have tensile strengths of more than 0.5 X 106 psi which is still only one-third of that of iron or sapphire whiskers, and compares with boron in filament form, although the specific strength of the steel wire would only be one-third of the latter. On the basis of specific strength drawn beryllium wire would be only slightly better than the steel, but would have about 6 times its elastic modulus (E) which is comparable to that of boron.