Low thickness knob panel in white sintered expanded polystyrene (EPS), to which a high impact laminated polystyrene (HIPS) film is coupled, obtained through a thermoforming process. The thermoformed film makes it possible to create retaining knobs that guarantee rapid installation and safe locking of the piping. It improves the mechanical resistance of the system and consequently the walkability during construction phases, and acts as a vapour barrier in the operating phase. The film is also shaped on the perimeter edges in such a way as to allow adequate overlap and a solid connection between adjacent panels, ensuring optimal sealing during the installation of the panels and the casting of the screed. The panels are suitable for lowered radiant systems (minimum total thickness 20 mm) fed by water for heating and cooling integrated into the structures according to the EN 1264 standard, ideal for energy redevelopment with limitations on existing heights and low inertia systems.