We all know exactly what we want under a tee shirt: a bra with smooth, seamless cups, minimal hardware and a smooth back. Racerback t-shirt bras have that and more. Racerback bras, which angle in close to the shoulder blades in either a T- or Y-shape and often have wide backs and straps, can prevent back fat and provide a smooth look under your tees. Most close in the front, too, which means no hardware poking against thin t-shirt material.
T-shirt bras are typically made of microfiber or some other super smooth fabric. There will be no seams on the cups and usually the sides are seamless too. They may also have light contouring or padding in the cups for modesty. Some tee shirt bras are made with convertible straps, so they can be worn in the usual way or as racerbacks.