The smooth cup bra is the biggest selling style of bra worldwide. In reality every woman needs at least one, as there is not one outfit in our wardrobes that wouldn't require a smooth cup bra to be worn underneath. This style will be completely seamless and without lace. The smooth cup bra is often made from a light foam or spacer foam to assist with support and shape and breathable against the skin. It can also come is a variety of different shapes to suit your personal needs, from plunge bras to balconette bras, push up bras - literally any shape you can think of is now made as a t-shirt bra.
A smooth cup bra and a t-shirt bra is exactly the same bra - it's a smooth cup bra to wear under t-shirts or under any body hugging tops. The "t-shirt bra" name was really adopted when we started wearing this style of bra under our t-shirts, but in the hand it is just a smooth cup bra, definitely not made from t-shirts!