Semi and full interpenetrating polymer networks of polydimethyl siloxane/polystyrene (PDMS/PS) and polydimethyl siloxane/polyurethane (PDMS/PU) were prepared sequentially. Characterization of the networks was made with swelling, differential scanning, calorimetry, stress-strain tests, dynamic mechanical thermal analyser, and scanning electron microscopy. The polymeric components are incompatible. However, considerable improvement in mechanical properties is observed by adding PS or PU to the PDMS host network.