Abstract: The present invention is directed to a rigid or semirigid, filled resin material having a continuous phase which is a matrix containing a complex crosslinked network having an unsaturated polyester-polyurethene containing resin having fine multisize reinforcing particles and dispersed filler particles dispersed therein. The polyester-polyurethene network of the complex crosslinked network may interact with other polymer networks in the continuous phase either by crosslinking or by forming an interpenetrating polymer network. The complex crosslinked network immobilizes the fine multisize reinforcing particles and reacts with at least a surface layer of the dispersed filler particles. The present invention is also directed to a process for preparing the above rigid or semirigid, lightweight resin material, and to a composition for use in this process.