Ken Sutherland reviews some of the filtration media made from nano-fibers. Energy conservation is, of course, a driver operating on all human activity, as is the need to reduce life-cycle costs. All of these drivers are effectively opposed to the most important driving force, namely reduction in the size of particles retained by the filter, or finer and still finer filtration. Almost all end-users of filtration are asking for more efficient processes, in which the levels of separation are set at ever smaller particle size cuts, whether for gas or liquid filtration. The ability of fiber manufacturers to produce materials in such small sizes has made a great difference to the filtration industry in its ability to separate very small objects from suspension, especially viruses, and hence enable micro-filtration to be employed for the sterilization of fluids without the need for heat.