From Mavics website: CERAMIC 2
What is it ?
Thermal shield that is 30 times harder than aluminum. This process has been improved on in 2000 for even greater strength.

Benefits :

Increases the coefficient of the friction between the rim and the brake pads. Reduces braking distance (50% in wet weather)
Superior resistance to wear
Reduces heat on rim

How :
A plasma beam torch spreads titanium and aluminum oxide powders on the sidewalls of the rim