Hot dogs may be labeled “skinless,” which means that the casing has been removed after cooking. Those with the casings left on may be labeled “natural casing” or “collagen casing.” Traditionally, sausages destined to be boiled, like frankfurters, were kept in the casing
to produce the juicy snap that some associate with a good hot dog. But if you’re grilling or griddling your hot dogs, keep in mind that the casings can become tough - especially the artificial ones.