Bag sealing equipment is categorized by the method used to seal a bag or pouch. Bags can be made out of different materials, such as plastic, paper, and cotton or other fabrics. Different types of seals are appropriate for different types of bag material. Bags can be sewn, pasted, or, in the case of plastic, heated and pressured shut. Cotton or other fabric bags can be used to ship loose items. Paper bags are usually used for loose items such as flour. Plastic bags are used for bread and merchandise bags. In addition, bag sealers can be used to apply shrink wrap to products before they reach the heat tunnel. Bag sealers do not exclusively seal pre-made bags; they can form bags as each closure is sealed. Bag sealers can be either automatic or semi-automatic. Automatic bag sealers automatically tuck flaps and seal the bag. Semi-automatic bag sealers require someone to manually feed the bag into the sealer to close the bag and tuck any flaps.