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hence hybrid / alu ala Mavic etc. excl. zipp
There's a difference between a hybrid rim (old Zipps or current low-end ones, Shimano Carbon Laminate rims etc.) where the carbon is the load bearing structure supporting the spokes and the aluminium deals with braking and tyre problems and a 'faired' rim (Cosmic Carbone, Flo etc.) where all the loads except aerodynamic ones are dealt with by the metal bit.
Generally clincher section harder to achieve with carbon hence hybrid / alu ala Mavic etc. excl. zipp etc.