Abstract: A flat composite board or panel for covering the vertical walls of rooms, which consists of a core (3) of synthetic foam produced in situ, an outer layer (2) having a decorative front surface (20) and a rear surface (21) to which the foam adheres, a synthetic layer (4) which adheres to the foam (3) by its front surface (41) and the rear surface (42) of which is covered with a web of fibres, the decorative front surface (20) of the board and its edges (12, 12') being covered with a sealed protective thermoplastic film (1) cooperating with the front surface (41) of the inner layer (4) to which it is secured at its ends (10) so as to form a sheath which limits the expansion of the foam and designed to be removed after the board has been fitted in position.