Aerogel. Researcher's hand balancing a sample of aerogel on a bunsen burner flame. This illustrates both the low density and the effective insulating properties of this material. Aerogel is a silicon- based solid comprising up to 99.9% air, commonly referred to as 'frozen smoke'. It is 1000 times less dense than glass and 39 times more insulating than fibreglass. This material has uses as building insulation in walls and windows, thus improving energy efficiency. Photographed in the Advanced Technologies Department of the Lawrence Berkeley National Laboratory, California, USA, in 1999.