Polycarbonate scratch resistance is a surface property, and the surface is not the polymer. A materials engineer once asked why the polycarbonate window on a packaging machine had gone hazy in eight months while the same sheet on a display stand two metres away was still clear. Both were 4 mm clear PC from the same delivery. The difference was a daily wipe with a dry paper towel on the machine, and a dry microfiber cloth on the stand.
Polycarbonate does not scratch because it is soft in the bulk; it scratches because the surface is soft. Bare PC sits around HB on the pencil hardness scale, roughly 2B to 3B on a Taber abrader at 500 cycles with a 500 g load. That is fine for an occasional touch and poor for anything that is cleaned every shift.
Polycarbonate scratch resistance: what a hard coat changes
A hard coat is a 3 to 8 micron cross-linked siloxane or acrylic layer applied to one or both faces. It lifts pencil hardness to 2H to 3H and cuts Taber haze to under 10% after 500 cycles at 500 g, depending on the product. It also adds a UV-stable surface that resists yellowing, which is why coated PC is specified for machine guards and signage rather than plain sheet.
The coat has limits. It is thin, so a deep gouge goes straight through it and the damage is more visible than on bare sheet, because the boundary is sharp. It also does not tolerate strong solvents: an alcohol wipe is acceptable on some products and not on others, and a ketone or an aromatic solvent will attack the coat within seconds.
Taber numbers and how to read a claim
A scratch resistance claim is worth checking for three figures: initial haze, haze after the stated cycles and the load used. A product quoting 5% haze without the cycles or the weight is quoting a number that cannot be compared. Standard practice is 500 cycles at 500 g with CS-10F wheels, measured to ASTM D1044 or ISO 3537.
Pencil hardness is the cheaper test and the one buyers use on incoming inspection. It is a pass or fail at a stated grade, not a precise measure, and it varies with the operator. Use it as a quick screen and rely on the Taber report for the specification.
Where uncoated PC is still right
Uncoated sheet wins on price, on formability and on impact performance at low temperature. A guard that will be thermoformed into a complex curve is usually bought uncoated, because the coat cracks when stretched. A large volume part with a short service life does not need the premium. The mistake is to buy uncoated sheet for a surface that gets wiped a hundred times a day.
The applications where a coated surface pays back, including the machine guard specification and the thickness ranges involved, are covered in our guide to hard coated polycarbonate for machine guards.
Cleaning is where the coat is protected or destroyed. Rinse with water first, wipe with a soft microfiber cloth and a neutral detergent, then rinse and blot dry. Never wipe dust off a dry surface, because the grit in the dust is what produces the fine haze marks that look like a material failure.
Tell us the cleaning frequency, chemical exposure and panel size at oversales@rpplexiglass.com, and we will quote hard-coated polycarbonate with the Taber report for the grade and thickness you need.
Frequently Asked Questions
How scratch resistant is polycarbonate?
Bare polycarbonate is around HB pencil hardness and abrades visibly under repeated dry wiping. A hard-coated sheet reaches 2H to 3H and holds haze under 10% after 500 Taber cycles at 500 g, which is the grade to specify for anything cleaned daily.
What is the difference between coated and uncoated polycarbonate?
The polymer is the same; the surface is not. A hard coat adds 3 to 8 microns of cross-linked layer that resists abrasion and UV, at roughly 20 to 40% price premium. Uncoated sheet is more formable and cheaper, so it suits short-life or thermoformed parts.
Can I polish a scratched polycarbonate window?
A light haze on bare sheet can be polished out with a plastic polish, though the area will never match the original surface exactly. A scratched hard coat cannot be polished back, because the coat is only microns thick and polishing removes it. Replace the panel instead.