Abstract: An integral seal member is formed across the outlet in the neck of a tamper evident, thermoplastic container by adding to the thermoplastic material such as polyethylene, 3% to 16%, and preferably about 8% by weight, of an anhydrous solid inorganic particulate additive such as an anhydrous siliceous material or calcium carbonate so that the material becomes brittle enough that the seal member tears cleanly from the neck within the confines of an undercut at the interface between the seal member and neck. Torque is applied to the seal member by providing in the top of a conventional screw cap which forms a resealing closure for the container once opened, a recess with serrations which, when the cap is removed and turned upside down, engage serrations on the peripheral edge of the seal.