The invention relates to a quick-operating door designed for opening and closing an aperture in a partition including: a support structure including in particular two vertical jambs (2) above which is a shaft driven by electromechanical means, each of the two vertical jambs (2) having an outer planar bearing surface (6) and a slideway (5), and a flexible curtain (4) designed to occupy a closed position in which the curtain (4) blocks the aperture and an open position in which the curtain (4) clears access to the aperture, the curtain (4) incorporating at least two transverse reinforcing bars (19) provided, at each of the ends thereof, with a tip in the form of a crank which engages with the guiding slideway in each jamb. According to the invention, the door has at least one transverse section (22) of the curtain (4) delimited by two transverse reinforcing bars (19) including two panels (23) connected to one another by means of a hinge (24), each panel (23) consisting of at least two strips (25) of a flexible material between which is inserted a layer of material stiffening, weighting and insulating said panel (23) for the purpose of keeping the transverse section (22) bearing on a planar surface (6) of each jamb (2).