Which coating process involves no external moisture or solvent?

Compression coating is the coating process that involves no external moisture or solvent. This method entails applying a layer of coating material directly onto a core tablet by using mechanical pressure during tablet compression. Given that the process relies solely on the inherent properties of the ingredients and compressive forces, there is no need to incorporate solvents or moisture, making it unique among coating techniques.

In contrast, other coatings often require some form of liquid as a vehicle for the coating material. For example, sugar coating uses syrup and may involve multiple layers of application with moisture, while film coating typically employs a solution or suspension that contains both a polymer and a solvent to form the film as it dries. Enteric coating also involves the use of solvents to apply materials that are designed to withstand acidic environments and dissolve in alkaline conditions, so the absence of moisture or solvents is a defining aspect of compression coating in this context.