Self sealing cap construction

Claim 1

AN ALL-PLASTIC MOLDED CAP COMPRISING A BODY HAVING A TOP PANEL PORTION AND A DEPENDING SKIRT PORTION, RETAINING MEANS ON THE INTERIOR OF SAID SKIRT PORTION FOR ENGAGING RETAINING MEANS ON A CONTAINER SO AS TO RELEASABLY SECURE SAID CAP IN SEALING RELATIONSHIP THEREON, A FLEXIBLE ANNUAL SEALING FIN BEING ELONGATED IN RADIAL CROSS-SECTION PROJECTING DOWNWARDLY AND INWARDLY INTO THE INTERIOR OF SAID CAP FROM ITS INTERGRAL CIRCUMFERENTIAL CONNECTION TO THE CAP BODY ADJACENT THE JUNCTURE OF SAID TOP PANEL AND DEPENDING SKIRT PORTION, AND CIRCUMFERENTIAL SHOULDER MEANS HAVING A BOTTOM ANNULAR SEALING SURFACE ON THE UNDERSIDE OF SAID TOP PANEL PORTION AND DEFINDING THE INNER SIDEWALL OF AN UPWARDLY EXTENDING ANNULAR RECESS LYING ABOVE SAID SEALING FIN, SAID ANNULAR SEALING SURFACE BEING SEALINGLY ENGAGED BY THE FREE INNER END OF SAID SEALING FIN WHEN SAID CAP IS SECURED IN SEALING ENGAGEMENT ON A CONTAINER WHEREBY THE UNDERSIDE OF SAID SEALING FIN FORMS A SEAL WITH THE RIM OF SAID CONTAINER AND SAID SEALING FLANGE FORMS THE FLEXIBLE BOTTOM WALL OF A SEALED AIR POCKET LYING ABOVE SAID RIM AND FORMED BY SEALING OF SAID ANNULAR RECESS.