Abstract: The open end of a plastics bag or like container is sealed by inserting the open end into the mouth of a sealer which welds the plastics film by the application of heat and pressure. Upon detection of the presence of a bag in the mouth a control unit initiates a sealing cycle. The user has available a film selection switch, linked to the control unit, to enable different film materials to be sealed satisfactorily. The sealing pressure, the sealing temperature and the duration of the sealing action are parameters which affect the sealing. These are independently controllable and presettable to cater for different film materials. The choice of the switch setting causes the control unit to initiate a sealing cycle with appropriate values for each of these parameters.