Abstract: A method of applying a moisture barrier seal to a fiber optic coil includes mounting a fiber optic coil in a vacuum deposition chamber, so as to expose a large exterior surface area of the fiber optic coil to an interior portion of the deposition chamber. The method further includes reducing the air pressure within the chamber to a value that is less than ambient pressure outside of the chamber. The method further includes introducing a vapor form of a non-porous material, preferably parylene, into the chamber. The vapor form of the non-porous material changes into a solid state upon contact with the fiber optic coil, so as to form a conformal coat on the fiber optic coil.