Abstract Experimental studies were made of the temperature and frequency relations of the complex elasticity modulus E and the tangent of mechanical loss angle tan δ of polyurethane acrylate filled with quartz powder. The concentration and the size of filler particles were varied. Results were analysed by the Williams-Landel-Ferri method using the concept of free volume. It was shown that the addition of a filler creates new relations in mechanical behaviour. On increasing the concentration of the filler in particular the actual flexibility decreases in the same way as on increasing the frequency of deformation.