The present disclosure relates to a tool used to producing anatomical phantoms. The tool includes an inner flexible mold which sits inside a rigid, thermally conductive outer shell. The rigid shell may be made out of aluminum. The silicone mold and thermally conductive shell both include at least two interlocking components. The shell is held together by a locking mechanism which can expand upon internal pressure. An anatomical phantom is produced from polyvinyl alcohol hydrogel by freezing and thawing a PVA liquid precursor in the silicone mold and demolding it.