The peanut butter an jelly sandwich, (PB&J), also known as a peanut butter and jam sandwich in the UK, Canada and Australia, is a sandwich that includes a layer of peanut butter and either jelly or jam on bread, commonly between two slices. Jars of pre-mixed peanut butter and jelly are commercially available for making these sandwiches. It appears to have been invented by GIs during World War II. The sandwich has the advantage that it does not contain any perishable ingredients, so it does not require refrigeration in hot weather, making it suitable for lunch bags. The peanut butter and jelly sandwich is very popular with both adults and children in the US and Canada. A 2002 survey showed the average American will have eaten 1,500 of the sandwiches before graduating from high school.