Protective and conventional fabrics are being investigated with emphasis on comfort as well as aerosol and chemical protection efficacy. Broad assault protection is assessed by measuring aerosol barrier efficiency using aerosolized polystyrene latex spheres and by measuring chemical protection using ASTM Standard Test Method for Resistance of Protective Clothing Materials to Penetration by Liquids (F-903) with acetone, methanol and sodium hydroxide solution. Comfort impact is assessed by the permeability index, im, which is the ratio of the thermal to evaporative resistance of the fabric normalized to the same ratio for still air. These data indicate that particulate penetration is a function of fabric structure and particle diameter. They verify the theoretically derived mechanisms by which fabrics trap particles in aerosols: larger particles are trapped by impact with fiber surfaces, while smaller particle penetration is governed by diffusion processes. Results of these tests define a “window of opportunity” where both barrier efficiency and permeability index might be jointly optimized for the benefit of the wearer.