Alloys are mixtures of a metal with other elements, the precise combination being governed by the required properties. Alloys are generally considered to be metallic in nature i.e. they have good thermal and electrical conductivities).
Alloys can be manufactured by various routes, the most widely used being to melt the constituents together and to cool the resultant mixture to form a single or multi-phase solid.
Foam - A low density, permeable structure of cells and continuous ligaments offering a high surface area to volume ratio, and also a high strength to weight ratio. Owing to the nature of this material, dimensions are nominal.