Strapless bras are especially important for special occasion dressing and those warm weather months when tube tops and strapless sun dresses are most popular. Strapless bras are designed to stay put without straps through the use of a wider band, boning under the arms and center front, silicone strips along the inside to prevent slippage and taller underwires for more support. A strapless bra without underwires is called a bandeau. It offers no significant support and is recommended only for the smallest of cup sizes.