Abstract: The invention relates to an apparatus for heat-strengthening glass sheets. In a heat-strengthening station (3) down-stream of a heating furnace the cooling rate of a glass sheet is retarded by means of plates (9, 11), which are set above and below a glass sheet and return some of the thermal radiation back to a glass sheet and slow down convection. Thus, a glass sheet can be heat-strengthened by chilling it at a certain controlled cooling rate. In order to make also the lower plate effectively return some of the termal radiation applied thereto despite the rolls fitted in between, the top surface of lower plate (11) is made highly reflective to thermal radiation and further corrugated in a manner that the ribs of corrugations extend between the rolls close to a glass sheet.