A technique is presented for the production of polymer-based phantom materials from solid polymer powders and various compounds added to adjust x-ray attenuation. After mixing of the finely grained components, the samples are solidified by a sintering process under vacuum. The method described allows a flexible and inexpensive production of phantom materials. Photon attenuation and density can be adjusted by suitable choice of base polymers and additives to mimic a large range of soft tissues and water.