Porous polymeric composites containing hollow microspheres such as hollow organic microsphere (HOM) and hollow glass microsphere (HGM), respectively, up to 50vol% were prepared by a UV-radiation photo-curing process. The non-porous sample was also prepared as a reference material. The comparative study on measured and theoretical thermal conductivity (k) revealed that HOM composites were in a category of the internal porous material (EMT model < k < parallel model) with spherical pore structure. In case of HGM composites which were considered as three-phasic material composed of bulk HPU matrix, thermal conductivity of HGM composites could be perfectly predicted by Felske model. From dynamic mechanical measurement, tensile and compression properties, it appeared that mechanical characteristics of hollow microspheres played an important role in storage modulus, T-g, and mechanical properties of composites. Especially, the incorporation of HGMs leaded to the reinforcement with increasing volume percentage of HGM in composites.