Piping BagA piping bag is a conical shaped bag made of cloth (often cotton), plastic, nylon, canvass, or plastic-lined cotton, filled with icing, dough, pastry or cream and used to dispense the contents, usually in a decorative fashion onto cakes, baking paper to be baked or pies. Each bag has a small opening at the bottom of the cone and a large one at the top. Some bags have a coupler at the smaller hole that looks a bit like a screw, onto which you can fit various decorating tips.
Choice of decorating tips, which are typically made of plastic or metal, is highly variable. They come in star and flower shapes, and in a variety of different opening sizes. The basic tip has either a round opening, or just a semi-oblong one. If you have the type of bag that doesn't have the coupler, you merely inset the tip into the smaller hole, from inside the bag, load in your frosting or other semi-solid food, and are ready to pipe and decorate to you heart's content. Though you can be extremely elaborate in your choice of piping bag tips, if you just want basic piping you may be able to buy just a few. Alternately, you can buy a set of tips that give you a lot of different options.
These bags are meant to be used repeatedly, and can be washed. Lightweight plastic or disposable piping bags can be handy too, particularly if you're decorating or piping food on the go, or don't plan to do a lot of decorating.
It is possible to make your own temporary piping bag, and actually some find this much easier. The easiest method for creating a piping bag is to use a large plastic, resealable bag. Cut a hole in the bag at one of its bottom corners, just large enough for the decorative tip to fit. This will easily allow you to easily pipe and decorate, though it usually only works for one use.