D(denier) indicates the thickness of fabric, and typically regular stockings have 20D, while opaque student stockings have 80D or so.
40D is not too thin, yet slightly see-through. They are designed to correct the leg shape.
SOFT & DRY
Double cloth weave with 100% cotton
They wick the sweat away from your soles
The cushioned soles reduce the fatigue of your feet.