Poly(urea urethane) (PUU) with a poly(dimethylsiloxane) soft segment was synthesized. Different types of conductive fillers-carbon nanotube (CNT), silver-coated carbon nanotube (CNT-Ag), and nickel-coated carbon nanotube (CNT-Ni)-were blended with PUU to form partially conductive polymer composites. The results showed that highly conductive metals could improve the conductivity of CNTs significantly. When the filler contents were 3, 4, and 5 parts per hundred parts of resin (phr), the PUU/CNT composites possessed electromagnetic interference shielding effectiveness (SE) at 8.5, 28.4, and 26.0 dB as the electromagnetic wave frequencies were 12.3, 16.2, and 15.9 GHz, respectively. SE of the composites that contained CNT-Ni and CNT-Ag increased with the filler loading. At the same modified-CNT loading, the CNT-Ni-filled composites had a higher SE than those filled with CNT-Ag. Tensile stresses ranged from 5.7 to 15.6 MPa (a 177.3% increase) when the CNT concentration reached 8 phr. (C) 2004 Wiley Periodicals, Inc.