The hydrophobic properties of tetramethoxysilane (TMOS)-based silica aerogels by incorporating trimethylethoxysilane (TMES) as a synthesis component, are described. The molar ratio of TMES/TMOS (M) was varied from 0 to 4.0 by keeping the TMOS, methanol (MeOH), water (H2O) and ammonium hydroxide (NH4OH), molar ratio constant at 1:14:4:3.7 X 10(-3). The hydrophobic properties of the aerogels were studied using contact angle measurements, infrared spectroscopy and thermal analysis. The contact angle, theta increased from 100 to 140degrees for M = 0.5 to 4. While the volume shrinkage of the aerogels increased whereas the bulk density decreased with increased M values. The hydrophobic aerogels are thermally stable up to a temperature of 300degreesC and above this temperature the aerogels become hydrophilic. (C) 2002 Elsevier Science Ltd. All rights reserved.