PVC (Polyvinyl Chloride)

Polyvinyl chloride, almost always shortened to PVC, is the third most produced synthetic polymer in the world after polyethylene and polypropylene. It was discovered accidentally in the 19th century but did not become commercially significant until the 1920s when chemists at BF Goodrich worked out how to plasticise it into a useful material. Today PVC turns up everywhere from drainage pipes and electrical conduit to vinyl flooring, hospital tubing and the sign panels you see in every shopping centre.

In a fabrication context, PVC comes in two main forms that you need to think of as different products. Rigid PVC, sometimes called uPVC for unplasticised PVC, is a hard dense sheet with high chemical resistance and excellent dimensional stability. It is the material used for chemical ducting, fume cabinets, tank construction, switchboard backing and acid resistant industrial work. The density is around 1.4 g/cm3, which is heavier than acrylic or polycarbonate and reflects the chlorine content. Rigid PVC sheet is typically supplied in grey or white, with custom colours available on order.

Foamed PVC, sold under brand names including Foamex, Sintra, Forex and Komatex, is the lightweight, easy to cut signage and display version. It is made by extruding PVC with a chemical foaming agent so the inside of the sheet is a fine closed cell foam while the outer surfaces remain smooth. The result is a sheet that has the same look and feel as a dense rigid plastic but at half the weight of an equivalent thickness of solid PVC. Foamed PVC is the standard substrate for real estate signs, A-frame signs, exhibition panels, retail POS displays and any application where a flat, paintable, printable sheet needs to be cut to shape quickly. The most common thicknesses are 3, 5 and 10 mm, in white as standard and a range of colours on order.

Both forms share PVC's two headline properties. The first is inherent flame retardance. PVC contains around 57 percent chlorine by weight, and chlorine atoms interrupt the combustion process. The result is a polymer that is genuinely self extinguishing, meaning if you hold a flame to a PVC panel and remove it, the flame dies out rather than spreading. This is why PVC is the default plastic for electrical conduit, ducting and any application where fire performance is part of the specification. The second property is chemical resistance. PVC tolerates acids, bases, salts, alcohols and most common cleaning chemicals far better than ABS, polystyrene or acrylic. It is the standard ducting material for industrial fume extraction systems and the standard tank material for many acid storage applications.

Where PVC trades off these properties is temperature and impact. The maximum continuous service temperature is around 60 C, which is lower than just about every other engineering plastic we work with. Above 60 C, rigid PVC softens and starts to lose its mechanical properties. This rules it out for hot water pipework, oven and steam applications. PVC is also not particularly tough. It is rigid and dimensionally stable, but it will crack rather than bend under sharp impact, particularly in cold weather.

The most important rule in a fabrication shop is that PVC must never be laser cut. The chlorine in the polymer breaks down into hydrogen chloride gas when heated by a laser beam. Hydrogen chloride combines with moisture in the air to form hydrochloric acid, which corrodes the laser optics, the cutting bed, the extraction system and anything else metallic it touches. It is also seriously harmful to operators. PVC is cut by CNC router, by table saw, by guillotine and by knife (for thin foamed grades), but never by laser. We are strict about this rule in our shop, and you should be too if you are working with the material.

Pricing for PVC is at the low end. Foamed PVC is among the cheapest sign substrates available, comfortably below acrylic, ACP and aluminium signage panels. Rigid PVC sheet is similarly affordable for the performance it delivers in chemical service. Standard sheet sizes are 2440 x 1220 mm and 3050 x 2030 mm, with thicker grades available in smaller standard formats.

Environmentally, PVC has a complicated reputation. The chlorine content makes it harder to recycle than polyolefins, and burning PVC waste produces hydrogen chloride and dioxin precursors if combustion is not properly controlled. On the other hand, PVC pipework and conduit installed in the 1960s and 1970s is still in service today, which is a meaningful argument for the longevity of the material. From a fabrication perspective, the responsible approach is to use PVC where its specific properties (flame retardance, chemical resistance, low cost) genuinely match the application, and to choose alternatives where they do not.

When not to use PVC: anywhere clear is needed (use acrylic or polycarbonate). Anywhere temperatures climb above 60 C (use polypropylene or polycarbonate). Anywhere impact resistance is critical (use polycarbonate or ABS). And anywhere a laser is the only available cutting tool (use anything else).