There are two methods of making bags - sideways or lengthways.
With this method, bags are produced on a machine using a hot knife which simultaneously cuts and seals the film to form the sides of the bag. The bottom of the bag is formed by folding the film.
Using this method, layflat tubing is sent through a machine. A hot bar makes a seal across the tube whilst simultaneously a sharp blade cuts the film below the seal. The seal therefore forms the bottom of the bag and the folds of the film form the sides. These are known as bottom-weld (or end-seal) bags.