Tee shirts come in so many styles--including sleeveless and tank, that a racerback bra can become a wardrobe necessity. Racerbacks angle in toward the shoulder blades with straps that may also sit closer in on the shoulders. The backs are either Y- or T-shaped and are often wider than typical backs, providing additional support.
T-shirt bras which are racerback will have smooth cups that are seamless and usually made of microfiber. The sides may be seamless too. The racerback construction, often combined with wide straps and back, can prevent backfat, smoothing you both front and back. If you wear your tees for exercise and sport, racerback bras can provide a greater range of motion, feeling less restrictive than conventional bras.