Vinyl Fence Co-Extrusion vs Mono Extrusion
Co-extrusion and mono-extrusion are the processes normally used in the production of all types of PVC/Vinyl Fence. The American Society for Testing and Materials (ASTM) has specifications for each product line. The buyer should be aware of which specifications are being used by the extruder. Some say Mono-Extrusion is better, some say Co-Extrusion. Take a look at the argument below and you decide.
Monoextrusion is the original way fence and even siding is made. Mono-extrusion is a process that injects a U.V. protector in the entire profile, having 100% coverage. Now most fence companies use co-extrusion because of cost, which is extruded with a capstock (the outer layer) and a substrate (the inner layer). Using co-extrusion causes the profile to have ONLY 20% coverage of U.V. protection, which is the capstock and is only paper-thin. It is easy to understand the differences if you think of mono-extrusion as being solid gold and co-extrusion as being plated gold, in time the outer layer will wear off and the fence profiles will begin to become brittle, crake and peal.
The co-extruded fence profile is made out of two concentric streams: an outer stream, called the capstock, containing the ultraviolet inhibitor and an inside stream, called the substrate with reduced ultraviolet protection. These two streams are chemically attached to each other under great pressure and temperature forming one continuous stream. These two streams appear to be layers, however they can not be separated. Co-extrusion demands a higher investment in equipment, tooling, training and overall manufacturing sophistication, but it significantly lowers material costs. In order to make the product even more affordable, many manufacturers make the inside layer out of reground material (rework) that may be a different color than the outside layer. This does not affect the product’s performance as long as there are no recycled materials used. The lower cost of co-extruded vinyl creates a slightly more affordable product without sacrificing quality. In the mid 90s, only a few manufacturers in the vinyl fence business were co-extruding. Today, a majority of the vinyl extrusion companies co-extrude. These are reputable companies that back their products with lifetime warranties, meeting ASTM vinyl fence standards. Some mono-extruding manufacturers warn that since co-extrusion can result in a different color of substrate material, a scratch on a co-extruded fence will reveal the substrate color-much like a scratch on a car will reveal the undercoat color. However, quality co-extruders make the outside layer thick enough so that a scratch will not penetrate through to the substrate layer. You cannot “key” your way through to the substrate the way you can with a car; the top stream or “layer” is just too thick.