Antireflected polyester films and low-iron glass sheets have values of solar transmittance that are substantially higher than those of their untreated counterparts. The plastic films utilize coatings to reduce losses due to surface reflectance and the glass is made with low levels of impurities to reduce absorption within the material itself. In this paper, we discuss the optical and thermal properties of these materials and derive the solar and thermal characteristics of windows incorporating high transmittance glazing layers. Comparisons among these and other types of windows are made on the basis of net energy use for residential buildings in winter.