Raw materials. All vinyl products are made from a unique combination of vinyl resin and various additives that give these products their particular properties. For more information on the vinyl resin process, see the general vinyl section. Every formulation is different, and most are proprietary. Some of the additives commonly used in vinyl siding and accessories include:
•Colorants, which determine the color of the siding.
•Ultraviolet (UV) protectants, which provide the siding with colorfastness even under daily direct sunlight.
•Stabilizers, which help maintain the siding's rigidity.
•Impact modifiers, which help keep the panels from denting or breaking under impacts such as hail.
Processing/fabricating. Once the additives have been combined with the resin, the resulting material is called vinyl compound and is in pellet form. In the next stage of manufacturing, the compound is extruded, formed into various shapes and cut into various lengths. Most siding accessories are manufactured in much the same way, but are formed differently after leaving the die. As is the case with most vinyl products, vinyl siding and accessories are ground up and reused if the manufacturer determines them to be off-spec in any way, leaving very little resulting waste. Because vinyl is a thermoplastic, it can be reheated and reprocessed without loss of physical properties, except for UV stability. For this reason, manufacturers extrude vinyl siding with virgin topcoats and use recycled material in the substrates. In some cases, vinyl siding is co-extruded with a thin acrylic topcoat, which improves the product's weatherability. After extrusion, vinyl siding and accessories are inert and chemically stable. Colorants and other additives are bound within the material, and although outdoor exposure may cause changes over time, consistent performance will continue.