Many different fill materials for ceramics have been used since the 19th century. However, very little scientific research has been carried out to assess their compatibility with the original ceramic and their subsequent behavior in various climatic conditions. For this reason, different fill materials in ceramic molds have been tested under adverse thermal conditions. Evaluations of other properties -- such as workability, reversibility and health safety factors -- were also made. The results indicate thixotropic epoxy paste laminated with acrylic modeling paste possesses superior properties for fill materials.