this invention is an acoustic device protected by an acoustically transparent low water permeability encapsulant made from an acoustically clear polymer such as polyurethane . high aspect ratio clay nanoparticles are positioned in the substrate in overlapping layers with layers of the substrate interposed . the invention also provides a method for forming an acoustically transparent low permeability encapsulant about an acoustic device . the method includes treating high aspect ration clay nanoparticles to make them organophilic . the treated nanoparticles are then mixed in a polymer resin in such a way as to form an intercalated mixture . a curing agent is added to the mixture , and the mixture is allowed to set . when set the resulting intercalated mixture produces an acoustically clear , low permeability polymer coating .