Abstract: An exhalation duct is formed from a gas impermeable covering layer having acer material extending through the length of the duct to define a substantally cylindrical opening. A lower end of the duct is formed with a plurality of exhalation holes or openings in the covering layer and an elastic end receiving the air supply hose of a self-contained air supply breathing apparatus. The upper end of the exhalation duct seals to an exhalation valve of breathing apparatus to direct exhalation air from the mask, entirely through the duct, for discharge through the holes formed in the lower end. In operation, the lower end of the exhalation duct is positioned within the torso area of a protective hood jacket to prevent internal fogging of the hood jacket mask.