Filters are often used to collect bioaerosols because of their simplicity and low cost. Filter collection is especially useful for personal bioaerosol sampling since they are light and unobtrusive. Filters can be preceded by a size-selective inlet, such as a cyclone or impactor, to remove larger particles and provide size-classification of the bioaerosol particles. Aerosol filters are often described using the term "pore size" or "equivalent pore diameter". Note that the filter pore size does NOT indicate the minimum particle size that will be collected by the filter; in fact, aerosol filters generally will collect particles much smaller than the nominal pore size.