Sunglasses lens coatings explained: hard coat, anti-reflective, hydrophobic and mirror

A sunglass lens is a stack, and most of what is in the stack you cannot see. The tinted lens itself sits in the middle, with the polarizing film laminated inside it or coated on. On top go up to four coatings, each with one job. A hard coat resists scratches. An anti-reflective layer on the back stops light from behind you bouncing off the inside of the lens into your eye. A hydrophobic layer makes water bead and smudges wipe off. And a mirror on the front reflects a share of light before it enters. The first is on almost every lens. The second is the one worth asking for. The third is a convenience. The fourth is a look with a function.

Hard coat

Plastic lens materials are soft. Polycarbonate scratches with a fingernail; tri acetate cellulose is not much harder. A hard coat is a thin, clear, harder layer applied over the lens that takes the wear instead. Nearly every plastic sunglass lens has one, and it is why they survive at all.

It is not scratch-proof. Grit under a dry cloth still scratches it, which is why our cleaning post says rinse first. But it is the difference between a lens that lasts years and one that hazes in a season. Our scratch post explains why a scratch through the hard coat cannot be polished out.

Anti-reflective, on the back

This is the coating people do not know to ask for. Stand with the sun behind you. Light hits the back surface of your lens, reflects off it, and goes straight into your eye. On a dark lens that reflection is bright enough to see: a ghost of your own eye, or of the scene behind you, floating in the view. It is distracting on the road and tiring on water, where light comes from everywhere.

An anti-reflective coating is a thin film tuned so that reflections from its two surfaces cancel each other out. Applied to the back of a sunglass lens, it removes the back-surface reflection almost entirely. It is standard on good sunglasses and absent on cheap ones, and the difference shows most on bright, open days.

It is fragile. Ammonia and alcohol degrade it; heat crazes it; our hot car post explains. It looks, when new, like a faint green or purple sheen on the back surface.

Hydrophobic and oleophobic

A hydrophobic coating lowers the surface energy of the lens so water cannot wet it: drops bead into spheres and roll off instead of sheeting. An oleophobic coating does the same for oil, so fingerprints and skin grease sit on the surface and wipe off in one pass rather than smearing.

Both are conveniences. On a boat or in rain they are real ones; a lens that sheds spray stays usable. They wear with cleaning, especially with harsh cleaners, and a lens that once beaded water and now sheets it has lost the layer. It does not affect the optics.

Mirror, on the front

A mirror is a thin metallic or dielectric layer on the front surface that reflects a share of incoming light before it enters the lens. Two consequences: the lens is effectively darker without a heavier tint, and your eyes are hidden. Our mirrored vs polarized post covers what it does and does not do.

It is the outermost layer on the front and the most exposed, and it is the first thing a dry wipe or a harsh chemical damages. Three of our five pairs are mirrored; the Ice Blue has the most reflective coating and needs the most care.

The stack, front to back

What we know about ours

The frame maker states the lens is tri acetate cellulose with a polarizing film and a UV-protective coating. It does not state a hard coat, an anti-reflective back or a hydrophobic layer, and we do not claim them. The mirrors on three pairs are visible and real. Every product page lists what is stated and what is not; our lens materials post covers the lens itself.

Frequently asked questions