Often used instead of a microporous filter, this system is particularly useful with paticulates, microorganisms and also pyrogens.? This makes it the companion filter of choice whenever pharmaceutical applications are involved, since a microporous filter does not remove pyrogens well.? It uses a membrane similar in design to a reverse osmosis system, except that its pores are slightly larger. Very often this filter is used to remove pyrogens from water that has already been purified of other contaminants, so a large amount of water passes through it.? Because of this, it will eventually plug if not carefully maintained.? In a properly designed system the ultrafilter is regularly washed clean of contaminants, and should be easily accessible to this kind of care.