A pastry bag (or piping bag in the Commonwealth) is an often cone- or triangular-shaped bag made from cloth, paper, plastic, or the intestinal lining of a lamb, that is squeezed by hand to pipe semi-solid foods by pressing them through a narrow opening at one end often fitted with a shaped nozzle, for many purposes including in particular cake decoration and icing. It is filled through a wider opening at the opposite end, rolled or twisted closed, and then squeezed to extrude its contents. Many differently shaped nozzles are used to produce cross-sections such as star, leaf, and flower-petal shapes; a simple circular nozzle makes round shapes and is also used for filling pastries such as profiteroles.
In addition to icing, pastry bags are commonly used to shape meringue and whipped cream, and to fill doughnuts with jelly or custard. They are used to form cream puffs, éclairs, and ladyfingers. Bags can also be used to shape savory foods such as filling for deviled eggs, whipped butter, and mashed potatoes (especially for Pommes duchesse).