The Ester form of Vitamin C consists of several molecules of Ascorbic Acid linked together to form one large molecule. Vitamin C Ester also contains metabolites of Vitamin C such as threonic acid that may increase its bio-availability.
Vitamin C Ester is claimed to be the most bio-available form of Vitamin C (Johnston, 1994). Nowhere in nature that humans would find ascorbic acid on its own. It is always bonded for stability to mineral.
Vitamin C Ester is Calcium Ascorbate which is a unique and exclusive form of vitamin C.