Carboxymethylcellulose or CMC is a gel of synthetic origin. It is a highly hygroscopic cellulose ether. It is often used in the form of its sodium salt, sodium carboxymethylcellulose.

As an excipient, cellulose powders are mainly used, often commercially referred to as "microcrystalline cellulose." It is a white powder, insoluble in water, but it disperses in water, forming a stable gel.