While 'padded' and 'molded' are sometimes used interchangeably in describing bras, there is a difference. Molded cups, made of one continuous piece of fabric, are seamless and perfectly smooth under t-shirts. But they are not necessarily also padded. T-shirt bras with no padding will not have bump-pads or other flexible foam, fiberfill or gel padding.
The molded fabric alone offers some support and shape and may also be lined for additional rigidity and modesty. This style of tee shirt bra is perfect when you want a smooth fit under tees and knits, but don't want to add any size or projection.