The ceramic membrane is free of metals and does not interfere with signals; the metal membrane contains silver, gold, etc., and may block signals.
Some low-end ceramic membranes may experience a decline in their heat absorption capacity under long-term exposure to sunlight, while the high-end multi-layer structure is more stable.
Enamel coating (i.e. ceramic coating on the surface of the paint) is a chemical bonding protective layer that is much more durable and long-lasting than waxing.