Postconsumer polymer recycling is a technology that involves many fields of science. The production of plastics has increased in recent years, and the products have many applications. Because of this, waste plastics are also increasing, causing many environmental problems due to the slow rate of natural decomposition of synthetic polymers. Polymer chemistry and process engineering are good tools for decreasing the problems caused by inappropriate polymer disposal. The subject of this work was the preparation of polymer networks based on recycled polystyrene (in the crystal form, PS; or in the expanded form, EPS) and polyurethane. The compositions were prepared by reaction between the polyurethanes (PU) components in the presence of recycled PS or EPS dissolved in the styrene monomer containing benzoyl peroxide as a free radical initiator. 1,4-butanediol (BDO) was used as chain extender for PU network. The compositions were characterized by the evaluation of mechanical properties, thermogravimetric analysis, and morphological analysis. The PS or EPS concentration used in the mixtures was in the 1-5 wt % range. The addition of PS or EPS changed the mechanical behavior as well as the final morphology of the compositions. The use of the PS/PU or EPS/PU network systems is a way of decreasing PS or EPS discards decreasing this environmental problem. (c) 2007 Wiley Periodicals, Inc.