Investigation of dust loading capacity for various assemblies of air filter media on atmospheric dust has continued using the small tester described in previous reports. The effect of fiber size and packing density in Fiberglas mat has been studied. The combination of very fine fibered glass mats now in use at Oak Ridge was given special investigation. Tests were made using a coarser mat as a prefilter and an economic advantage was showm for such protection. As a result of laboratory studies on gauze backed hand sheets a paper mill run is planned to make paper comparable to #6 now used by Chemical Corps for AEC filters but stronger and lower in cost In this run the paper will be made with a reenforcing gauze backing. Fabrication work is being carried on with emphasis on two special shapes of units both of which aim to simplify installation and removal and to give better protection to operating personnel when filters are being changed. These shapes namely the hollow cube and the circular will be described in detail with sketches and test data. A 950 CFM full scale model of the hollow cube has been constructed to demonstrate the practicability of the …