Coatings and filters
Hard coating
Optical glossaryCoatings and filters
A hardened protective layer that resists scratching. The foundation every other coating is built on.
Illustrative · the shape of the principle, not measured data
In more depth
Plastic lens materials are much softer than glass, so almost every lens is given a hard coat: a thin, clear, glass-like layer, cured onto both surfaces. It makes the surface far more resistant to fine scratches from everyday handling.
It also carries the layers on top. Anti-reflective layers are very thin and rigid; laid directly on a soft plastic they would crack as it flexed, so the hard coat is the foundation they need. No coating makes a lens scratch-proof — grit dragged across a dry lens will still mark it.
Related terms
Anti-reflective (AR) coatingMicroscopic layers tuned so surface reflections cancel. More light through the lens, no bright rectangles over your eyes, no headlight starbursts.Hydrophobic / easy-clean layerA slick top layer that makes water bead and smudges wipe away rather than smear.Residual reflectionThe faint color an AR coating still reflects — green, gold or blue depending on the layer design. A signature, not a flaw.