Abstract: The invention features a clean room and a chemical air filter suitable for use in the air handling system of the clean room directly upstream of high-efficiency particulate air (HEPA) filters. The chemical filter is of the pleated filter type comprising an air permeable, relatively thick web of non-woven fibrous carrier material of pleated form. The web includes a matrix formed of a large multiplicity of synthetic fibers and is characterized in that activated carbon particles are distributed throughout the web, bound in the interstices of the matrix in a manner preventing loss to the air of particles in quantity substantially detrimental to the performance of the HEPA filter. The activated carbon particles are of the type selected to remove the predetermined gas-phase contaminant from the air from the source. The invention also features a non-off gassing filter casing that may easily be installed into existing clean room air handling systems.