It's called Magic Sky Control, and Mercedes says it can reduce cabin temperatures by as much as 10C by blocking up to 95% of the energy generated by the sun.
This in turn puts less strain on the climate control system, helping to save fuel. Magic Sky Control also allows owners to adjust the amount of light entering the cabin.
It works by changing the position of tiny particles within the roof glass. When an electrical charge is applied, the particles separate, allowing more light in. Switch the current off and the particles come together to give more shade.
The change-over is controlled by a switch in the overhead console. Magic Sky Control will be offered for 'less than €2000' (£1725), says Mercedes.