be no more than approximately 0 017 inches thick and may be no more than about 0 009 inches thick and may be comprised of a very thin plastic or the like and may have a melting point temperature of at least about 200 degrees f such as a pert plastic for example additionally the very thin plastic coating 2 may comprise a plastic coating 2 that will not readily develop stress cracks via at least one of temperature and pressure changes an optional very thin paint coating 2 could also be used with similar advantageous heat transfer results and would may comprise a high gloss paint type that also could withstand at least about 200 degree f temperatures without impairment such a very thin coating 2 for a refrigerant to air heat exchanger which is not shown herein in its entirety as same is well understood by those skilled in the art may also be composed of a substance such as a tetrafluoroethylene resin ptfe teflon u00ae such as dupont teflon u00ae pfa having a thickness coating 2 of only about 0 003 to 0 004 inches or such as a fluroropolymer dip coating 2 another example of such a very thin coating 2 may consist of plasma polymerizing a fluoroethylene monomer such as tetrafluoroethylene in the presence of the desired exterior surface and depositing a fluoropolymer coating 2 of about 1 10 000 inch or less on the exterior surface another example of such a very thin coating 2 may be a triazine dithiol derivative or the like coating 2 fig5 is a top view of a.