A vent arrangement is provided to a mask to discharge exhaled gas from the mask to atmosphere. The vent arrangement is structured to diffuse the exhaust vent flow to produce less air jetting, thereby increasing the comfort of the patient and their bed partner. The vent may include a first wall, a second wall defining an outer perimeter, and a plurality of gas washout vent holes positioned between the first wall and the second wall, the vent holes having an inner edge positioned within the outer perimeter of the second wall.