T means Thread which refers to fiber, and the number indicates the sum of vertical and horizontal fibers in one square inch of fabric (see photo). The higher the Thread count, the denser the weave and the greater the fabric's durability.
D means Denier and it is a unit of measurement for the thickness of a thread. A lower denier means a finer fiber, while a higher denier means a thicker, more durable fiber. To calculate the Denier of a polyester fiber, a piece of 9,000 meters in length is weighed, and the resulting grams are the Denier of the fiber. Therefore, if a 9,000-meter-long polyester fiber weighs 210 grams, its Denier is 210.