Todays buildings consume more energy than any other sector of the U.S. economy. Improving insulation of building envelopes offers an important means to reduce energy consumption. Advanced building envelope materials that can dramatically improve energy efficiency are needed including innovative higher performing insulations (R8/inch or 30% higher R-value than existing materials). DOE seeks technologies that have the potential to contribute to a 50% reduction in energy demand of residential and commercial buildings at less than the cost of the energy saved. Aspen will develop a blown-in insulation product that comprises Phase Change Materials (PCM) integrated with aerogel insulation. The product will provide a simultaneous increase the thermal resistance and heat capacity of existing structures to conserve energy. With the combination of passive insulation of aerogels with the dynamic thermo-regulating ability of PCMs, the hybrid material will provide significant energy savings by reducing the need for HVAC cooling and by shifting energy peak loads from daytime towards cheaper night time. During this project Aspen Aerogels will design, develop, and evaluate a blown-in aerogel-PCM product for building cavity insulation retrofits and new construction, with high energy savings and minimal impact on the existing structure. The blown-in PCM aerogel insulation will offer over 50% improvement in R-value compared to existing blown insulations. This product will reduce energy consumption and peak-hour power loads, while significantly improving space savings compared to other retrofit solutions. To eliminate settling of the insulation, the aerogel will be designed to have adhesive properties under impact loading conditions during installation. The PCM-enhanced aerogel insulation will be non-settling, hydrophobic, water vapor permeable, fire retardant and durable, as well as easy to install using traditional insulation blowing equipment. The addition of PCM material to the aerogel will add a dynamic R-value to the aerogel that contributes to the energy savings and cost reduction. The proposed program will identify the effectiveness and magnitude of the blown-in insulation energy savings and the return on investment. An emerging Building and Construction market segment for blown-in aerogel insulation includes additional energy saving initiatives, such as passive houses and deep energy retrofits. Current retrofit designs require such excessive amounts of insulation that they limit implementation. Since the requisite volume of the aerogel-based insulation is so low, implementation of energy saving aerogel insulation is a paradigm shift in building retrofits. Conservatively, the B & amp;C energy retrofit market is expected to reach hundreds of millions of dollars in annual sales.