Abstract: A cap for a bottle having a tubular neck formed with an external screwthread and terminating at an annular rim surface has a cup-shaped body generally centered on an axis and formed unitarily with an end wall generally perpendicular to the axis. An annular skirt projects axially downward from the end wall and an internal screwthread in the skirt can mate with the screwthread of the bottle neck. A flexible annular web has an outer periphery joined to the skirt adjacent the end wall and an inner periphery secured to a seal ring. The web and seal ring are dimensioned to engage the rim surface when the cap is threaded onto the neck, and an antitamper ring is secured to a lower end of the skirt.