Elastic is normally applied either by sewing it straight on to fabric, or inserting it in to a specially created casing. There are many different types of elastic, and they come in different widths and thicknesses. It's easy to think initially that "any old elastic laying around will do", but use the wrong type and it can ruin the whole sewing project- so what are the different types, and what are they best used for?
Elastic is made by binding threads around an inner rubber core. The threads are bound either by weaving (=> woven elastic), braiding (=> braided elastic), or knitting (=> knitted elastic), and either polyester, cotton or nylon threads are used.