These film wraps are desirable for packaging food because they are much less permeable to water vapour and gases than paper and leaves and are chemically inactive with food. They are used to package both solid and liquid foods. Polythene bags are useful for dry products such as gari, sugar, coffee, and cocoa power, as the items remain dry for a long time if properly sealed. Since heat-sealing devices are not readily available to many vendors, the open ends of the bags are usually tied into firm knots after the food is inserted. Bread and other pastries are packed in polythene bags on a large scale.
Many vendors expose their products to the sun while sealed in the bags.
Moisture condenses inside the bags, and this facilitates mould growth. Sometimes air is blown into bags with the mouth to open them. This introduces vapour and microorganisms, which sets the stage for spoilage when foods are placed in the bags. Home-made ice follies, which are commonly frozen in plastic cups, and beverages such as nmadaa, normally served in calabashes, are now sometimes packaged in small polythene bags for sale. Iced water is also sold in plastic bags by some vendors in response to official directives aimed at curbing the unhygienic practice of using a single cup to distribute water to many customers.