The report summarizes the work that has been carried out within the project "B1 AEROGELS" as a part of the IEA SH&CP Task 18 "Advanced Glazing and Associated Materials For Solar And Building Applications".By providing at the same time thermal insulation and transparency the silica aerogel is a very attractive material for the purpose of improving the performances of windows. Nevertheless a lot of problems have to be solved on the way from concept to the developed product. The B1 Aerogels project deals with some of these problems.The objective of the B1 Aerogel project is:"To develop the scientific, engineering and architectural basis which will support the appropriate use of aerogels in windows, solar collectors and passive solar applications, with the aim of saving or producing thermal energy for use in buildings".This objective is in very good agreement with the general scope of task 18 but where Task 18 focuses on the development and use of advanced windows in general, the B1 Aerogel project is focused on the application of aerogels only.The scope of the aerogel project was to perform an evaluation of the aerogel material and to identify some of the strengths and weaknesses that can be expected of aerogel as a material for window applications. It was not a part of the project to make a further development of the aerogel material.The project was carried out in three main steps:1. Collection of information on aerogel production methods2. Measurements and evaluation of optical and thermal properties of aerogel as a material for window applications3. Construction of an aerogel DGU and measurement of key performance parameters. The goal for the aerogel DGU was to reach a Total Solar Energy Transmittance above 0.75 and a U-value below 0.5 W/m²K. These are values that can not be simultaneously reached by any other type of window.The project has been carried out in a cooperation with several other Task 18 projects: The aerogel project has collected and distributed aerogel samples for other Task 18 projects. The B11 and B13 have performed optical measurements on aerogel samples as well as on the aerogel DGU that was developped during the project. B12 and B14 have measured the g-value and the U-value respectively of the aerogel DGU.Furthermore calculations of the energy saving potential by using aerogel windows in selected residential and commercial buildings under different climatic conditions were carried out as part of the A2/A3 project.The B1 Aerogel project has been carried out with partition of the following nations: Denmark, Finland, France, Germany, Japan, Norway, Sweden and the United Kingdom.