Curtains commonly used in the agricultural ventilation industry were evaluated for air infiltration characteristics as a function of curtain material, closure overlap distance, and wind speed in a controlled and calibrated wind tunnel. Curtain material ranged from polypropylene to woven mesh with measured specific weights varying between 168 and 866 gm/m 2 (0.6 and 2.8 oz/ft 2 ). Curtains classified as breathable allow as much as 1243 m 3 /h–m 2 (68 cfm/ft 2 ) of infiltration air at wind speeds of 13.4 m/s (30 mph). For non–breathable curtains at wind speeds of 13.4 m/s, infiltration rates were reduced to 366 m 3 /h–m 2 (20 cfm/ft 2 ) for single–layer low–density curtains to essentially 0 m 3 /h–m 2 for multi–layered insulated curtains. Curtain closure overlap distances of at least 5.1 cm (2 in.) were found to drastically reduce infiltration at the opening. A non–breathable curtain that just reaches the top of the opening (i.e., 0–cm curtain overlap) can allow nearly as much infiltration air to enter as a breathable curtain.