microwave heating apparatus especially useful for heating and curing reinforced thermo - hardenable synthetic resins is disclosed . heating cells are formed by parallelepipedal enclosures , the walls of which are odd multiples of 1 / 4 the wavelength of electromagnetic energy being utilized for heating . adjustment means for adjusting the enclosure to minimize reflected power are mounted within the enclosure . a production line comprises a series of successive heating cells that are supplied from the same power source ; die structures between the cells can be used to form the material being processed .