Low-density nanoscale mesoporous composites may be readily synthesized by adding a colloidal or dispersed solid to an about-to-gel silica set. The silica sol can "glue" a range of chemically and physically diverse particles into the three-dimensional silica network formed upon gelation. If the composite gel is supercritically dried so as to maintain the high porosity of the wet gel,:a composite aerogel is formed In which the nanoscopic surface and bulk properties of each component are retained in the solid composite. The,volume fraction of the second solid can be varied above or below a percolation threshold to tune the transport properties of the composite aerogel and thereby design nanoscale materials for chemical, electronic, and optical applications.