Composite panels may be prepared using a moisture resistance additive having a formulation that includes a triglyceride having a saponification value of at least 150 and an iodine value of at least 35. The additive may be used in the form of a water emulsion. The water emulsion may be prepared by dispersing the components of the additive formulation under conditions sufficient to at least partially saponify the triglyceride. The moisture resistance additive can impart resistance to moisture absorption and thickness swelling to composite panels prepared therewith.