Abstract A LINEARLY EXTENDING SEAL OR WELD BETWEEN A PAIR OF HEAT SUSCEPTIBLE THERMOPLASTIC SHEETS ISPODUCED BY INTERPOSING THE THERMOPLASTIC SHEETS IN SUPERPOSITION BETWEEN A PAIR OF HEAT RESISTANT CONTROL SHEETS, AND SLIDING AN ELONGATED HEATING WIPER ALONG ITS AXIS IN CNTACT WITH ONE OF THE CONTROL SHEETS IN ORDER TO APPLY HEAT AND PRESSURE TO THE THERMOPLASTIC SHEETS WHILE COUNTERED BY THE OTHER OF THE CONTROL SHEETS. THERESULT IS A WELD CHARACTERIZED BY A TROUGH AT ONE FACE OF THE SUPERPOSED THERMOPLASTIC SHEET AND A RIDGE AT THE OTHER FACE OF THE SUPERPOSED THERMOPLASTIC SHEETS, THE TROUGH AND THE RIDGE BEING IN REGISTRATION AND THE REGION THEREBETWEEN BEING INTEGRATED. APPARATUS FOR EFFECTING THIS PROCESS AND PRODUCING THIS PRODUCT IS DISCLOSED.