What is Co-Extrusion?
Co-Extrusion is a more recent advancement in extrusion technology which brings 2 layers of PVC into play: The outer layer, or Cap Stock, contains a denser concentration of UV inhibitors. ASTM’s “Specification for Rigid PVC Exterior Profiles Used for Fencing” (F 964-94) requires that the cap stock layer be a minimum of 00.015” thick and a maximum of 20% of the overall thickness of the profile wall. It is important for the potential buyer of a Vinyl fence to determine what ASTM specification is being used by his potential extrusion supplier, if in fact any is being used at all, and to ensure that compliance is being verified regularly.
The inner layer, or Substrate layer, when produced with virgin raw materials, is essentially the same as the cap stock layer, but with a lowered concentration of UV inhibitors and color pigment.