BACKGROUND: One of the major problems facing biofilter operation is the long start-up periods, which is related to microbial adhesion in packing materials among other factors. In order to deal with this limitation, modifying a hydrophobic polymer with an additive containing hydroxyl groups was proposed to improve the water retention capacity of the material in the biodegradation of a mixture of hydrocarbon vapors in batch tests. RESULTS: The synthesized material with 40% by weight of hydroxyl-containing additive had a water retention capacity of 34%. The presence of hydroxyl groups was confirmed by absorbance at 1100 cm(-1) wave number using Fourier transform infrared spectroscopy analysis. Complete biodegradation of methyl ethyl ketone and toluene vapors were achieved on the sixth day whereas hexane vapors were degraded on the 14th day. The time required for the complete biodegradation of hydrocarbons with the modified polymer was at least 30% lower than that obtained with the non-modified polymer. CONCLUSIONS: The additive, a hydrocarbon containing hydroxyl groups, was able to modify the polymer's hydrophilic character. In addition, the additive improved the microbial growth and the attachment of microorganisms to the material; thus, it enhanced the biodegradation rates of hydrocarbon vapors. This makes the composite suitable for application as a packing material for biofilters. (C) 2010 Society of Chemical Industry