The purpose of this study was to test the performance of 48 experimental multilayer window treatments with respect to overall thermal resistance (R-value), both initially and as a function of time after 150-2400 uses. Following the R-value testing and analysis of commercially available multilayer treatments, the experimental treatments were constructed with the following variables: (1) fiber content and number of layers of batting, (2) fiber content of face and back fabric, and (3) stitching pattern. The results of the study indicate that window treatments can significantly reduce thermal energy losses from window areas. Analysis of the variables indicated that there was little difference with regard to R-value between the two face fabrics. Both cotton and polyester proved to be good insulators. The fiber content or doubling the thickness of the batting materials did not appreciably increase the R-value. Of the stitching patterns, edge provided the highest and onion the lowest R-value. The initial R-values of the treatments were not affected significantly after 2400 uses or the equivalent of daily operation for more than six years.