Vinyl siding is mostly made up of extruded polyvinyl chloride (PVC) that contains additives, such as:
- Colorant material used to create the many various vinyl siding color options.
- Acrylics and acrylate acrylonitrile added to the cap stock for durability, strength and fade resistance.
- Lubricants to allow the material to pass easily through the extrusion equipment.
In the manufacturing process, two layers of vinyl are extruded, one on top of the other. The material is still hot, so the layers fuse. The lower layer is called the substrate; the top layer is the cap stock. The layers are inseparable.