A filter for a gas mask has an elliptical or circular, convex shape to conform to the curvature of the wearer's face, or a planar shape. The filter comprises a double particulate filter element and a double adsorption filter element configured for axial airflow therethrough with a bifurcated flow pattern. The adsorption filter element comprises a granulated charcoal, a composite material having carbon particles combined with binder particles, or an immobilized bed of charcoal granules and EVA-coated fibers.