Why engineer porous materials?

A number of specific examples are briefly given for the use of pores in engineering materials: a porous ceramic to produce minimum thermal conduction; thin skeleton walls in silicon to produce photoluminescence; low dielectric constant materials. The desirable nature of the pores in fuel cell electrodes and sieves is described. Further examples are given in orthopaedics, prosthetic scaffolds and sound deadening and impact resistance materials. An attempt is made to describe the desirable pore size, whether open or closed, and the useful volume fraction. This short review does not deal with flexible foams.