the invention relates to compositions having low water vapor permeability prepared from protonated chitosan and lauric acid. in film form, the composite polymer can provide protection to enrobed substances from oxygen and other gases and to water and water vapor the chitosan-lauric acid films of the invention can be usefully employed as protective coatings to protect a base substrate from the deteriorative effects of moisture and air, including oxygen, and loss in quality due to water transmission. the films find particular use in protecting raw or processed food products from deterioration by water transmission and oxidation. the films of the invention have distinct advantages over many synthetic polymeric film substances presently in use, such as films prepared from polyvinyl chloride, modified acrylates, and olefins, because they are prepared from biodegradable substances. the starting materials are non-toxic and can be obtained from readily-available naturally occurring materials