Polymeric materials are being developed with renewable resources to promote industrial progress with environmentally friendly technologies. For this reason, polyurethane samples were prepared with 4,4'-diphenyl-methane diisocyanate (NCO/OH 1), eucalyptus tar pitch (biopitch), castor oil as a polyol, and dibutyltin dilaurate as a catalyst. These materials were reinforced with different contents of short sisal fibers (0, 2.5, 5.0, 7.5, and 10.0%) and were prepared by resin-transfer molding. The composites were characterized by IR absorption spectroscopy, thermal analysis (thermogravimetry and differential scanning calorimetry), impact resistance, scanning electron microscopy, and water absorption resistance. These materials showed hydrophobic characteristics, despite the addition of sisal fibers. (C) 2003 Wiley Periodicals, Inc.