There are many styles of brassieres, to be worn in a variety of situations and with a variety of outergarments. The degree of shaping and coverage of the breasts varies between styles, varying in both functionality and fashion, fabric, and colour, from purely utilitarian to sensual. Others include various accessory structures such as padding and 'underwiring'. Many bras will fall into more than one category, such as a maternity bra designed for facilitating access to the nipple, but also designed to provide the lift that a push-up bra would. Definitions are not always very accurate or exclusive (e.g. shelf bra). Currently underwired bras are the fastest-growing segment of the market.