an apparatus for thermally densifying thermoplastic articles , particularly those of the expendable type . the apparatus includes a chamber for placing the thermoplastic articles within , a heater for heating the thermoplastic articles placed within the chamber to a temperature effective for the thermal densification of the thermoplastic articles , a temperature sensor located proximate to the heater , and a controller for controlling the heater responsive to the temperature sensor , which is capable of providing a temperature within a range from about the temperature effective for thermally densifying thermoplastic articles to a temperature below the point of significant thermal degradation of the thermoplastic articles . a process for the thermal densification of thermoplastic articles are also provided .