polymer composition bags are located in a stack with the holes in the lips of lip bags engaged on wickets . when a stack of bags is so located , it is supported by an anvil , and a tamper foot comes down adjacent the anvil to clamp the stack of bags . a hot needle penetrates the lips on the stack of bags to tack - weld the bags together so that they may be handled as an integral unit , but bags can be individually removed at the bag - filling station .