One of seven articles forming a practical guide to HVAC for museums and historic renovation. Discusses the functions of filters in museums and art galleries. Discusses how filters work, filter testing and comparison, and different filter types and their construction. Discusses new filtration technologies and products, including molecular filtration, adsorption condensation, and chemisorption. Deals with testing of gas-phase filters.

Article appeared in the Practical Guide to HVAC for Museums and Historic Renovation, which was included with the vol. 41, no. 4, April 1999 issue.