A lid which has a bottom portion and an upwardly extending sidewall surrounding the bottom portion and which is to be removably fitted within the inside walls of a receptacle. The sidewall portion is formed with a plurality of longitudinal grooves, whereby when the lid is fitted into the receptacle,...http://www.google.es/patents/US4018355?utm_source=gb-gplus-sharePatente US4018355 - Inner lid of a receptacle for instant-cooking foods
Inner lid of a receptacle for instant-cooking foods
