What constitutes a pastry bag versus a piping bag, by definition, is that a pastry bag, being larger, must be held in your hands when piping, while a piping bag is held with the fingers only. Therefore, technically speaking, the size determines the name. However, in general, people referring to a pastry bag are speaking of a reusable bag made of canvas or other material; a piping bag is usually a handmade paper cone meant for a single use. These directions, combining the two, are for making a disposable pastry bag from baking paper. This is fast and easy to do and is a practical solution in many instances. I simply tear a sheet of baking paper in half when I need a bag, but you could certainly cut sheets ahead of time so you always have 12- × 16-inch (30- × 40-cm) pieces handy. In several European countries, including my own, Sweden, professionals are required by law to use disposable pastry bags when working with dairy products.
Tear a full sheet (16 × 24 inches/40 × 60 cm) of baking paper in half crosswise against the edge of a table. The cut edge will be a bit ragged, but this doesn’t matter. Set one piece of paper aside to use another time.
Hold the paper so that the rough edge is at the top (the opening of the bag) and fold the paper into a cone as you do to make a piping bag (Figures 1-15 and 1-16). See Figures 1-22 to 1-25 for a more detailed example.
To keep the bag from coming apart, fold up about 2 inches (2.5 cm) of the tip.