Abstract: The invention relates to an arrangement in an apparatus for forming a windscreen interlayer that includes a heating unit for heat treating a moving web. The heating unit includes individually adjustable radiation units for directing radiation towards the moving web and a radiation restriction device for suppressing the radiation output in desired areas. According to the invention, the radiation restriction device includes a board which is essentially perpendicular to the plane of the web, the board being aligned essentially in the travel direction of the web and positioned at the level of the radiation sources at its upper end and at a distance from the web at its lower end such that no direct radiation output is directed towards the desired area of the web from the closest radiators in operation.