The materials used for academic dress vary and range from the extremely economical to the very expensive. In the United States, most Bachelor and master's degree candidates are often only presented the "souvenir" version of regalia by their institutions or authorized vendor, which are generally intended for very few wearings and are comparatively very inexpensive. For some doctoral graduates, commencement will be the only time they wear academic regalia, and so they rent their gowns instead of buying them. These rented (or hired) gowns are often made of inexpensive polyester or other man-made synthetic fibre. In Britain, rented gowns are almost always polyester while Russell cord, silk, or artificial silk gowns are only available when bought. Undergraduate gowns are usually made from cotton or cotton and polyester mix and are relatively inexpensive to encourage students to own them.