The term 'pantyhose' is exclusively American, referring to the combination of 'panties' (an American term for women's undergarment) with hosiery. The one-piece pantyhose was a substantial improvement that appeared in the 1960's because it provided a convenient alternative to separate underwear and hosiery. In North America, the term tights is used to describe a garment similar to pantyhose, but which is thicker and more commonly worn by girls, dancers, and athletes.
Pantyhose are worn for a number of reasons. Sheer pantyhose that match the skin color of the legs can enhance the appearance of legs, making them look smoother. Darker pantyhose can enhance the legs by outlining the shape. Pantyhose also has practical use, as it can provide warmth in colder weather and let women go "bare-legged" even in the winter. Pantyhose can even enhance blood circulation by applying even pressure on the legs throughout the day.
Pantyhose are available in a wide range of styles. The sheerness of the garment, expressed as a numerical 'denier'/'dtex', ranges from 3 (extremely rare, very thin, barely visible) to 20 (standard sheer) up to 30 (semi opaque). The terms denier and dtex refer to the weight of the yarn in grammes at a standard length: for denier, it is 9,000, for dtex, 10,000 metres. Thus, 1 Denier = 1g of yarn when 9,000 metres long.
Pantyhose also come in a variety of colors, from gray/black or skin tone common in business wear to brightly colored styles fashionable among young women.
Most pantyhose are composed of nylon and spandex, which provides the elasticity and form fitting that this characteristic of modern pantyhose. Unfortunately, the nylon fabric is somewhat prone to tearing and it is common for very sheer hose to 'run' soon after snagging on something sharp.
Pantyhose worn for fashion have a standard construction. The top of the waist is a strong elastic. The part covering the hips (boxer/brief area) is composed of a thicker material than the legs. The gusset or crotch is also a stronger material, sometimes made of cotton. The legs of the pantyhose are made of the thinnest material which has a consistent construction down to the toes, which may be reinforced to guard against wear. To see details of how pantyhose are manufactured, check this site:
Interestingly, hose for the legs were a male fashion (for example among European and American aristocrats during the 16th Century), while women hid their legs from public view. This trend reversed, however, with men wearing pants and women exposing their legs. In the 20th Century, pantyhose have been marketed to women exclusively. However, in recent years some versions for men have appeared in the marketplace, touted for warmth as well as for appearance, improved blood circulation, and comfort.