Love this fabric. Ultra Aero is slightly dimpled this is to create less friction and superior aerodynamics when moving, but what we really like is that it is one of the coolest to wear in hot weather, it washes and wears superbly and it has firm stretch and recovery so keeps great shape. The 6 panel contour makes for excellent fit. A medium equates to a size 12. Sometimes it is not the glittery stuff that is special, these are pure gold!