Kato Polyclay has been developed by clay artist Donna Kato in conjunction with Van Aken. All colors are extremely durable, the colors either do not change at all or change only minimally. It doesn’t get sticky soft when handled and worked. When it is thin, it’s flexible, when it is thick, it’s rigid. Kato clay does require a bit more conditioning to use than other brands. New formula of Kato polyclay is now Phalate free!