What is an Eyeglass lens made of?
What is an Eyeglass lens made of?
Almost never glass — usually CR-39, polycarbonate or a high-index plastic, under several thin coatings.
The trade-off buried in the high-index sales pitch is the Abbe number, which measures how much a material splits light into colours. CR-39 has an Abbe number around 58 and is optically excellent; polycarbonate is about 30 and high-index plastics are lower still, which shows up as coloured fringes at the edge of vision in strong prescriptions. So the thinnest lens is not automatically the best one, and for a mild prescription it is usually the wrong choice. Glass lenses have almost disappeared from everyday eyewear because they are heavy and shatter, though they still have the best scratch resistance and optics.
Component by component
| Part | Material | Why that material |
|---|---|---|
| standard plastic | CR-39, an allyl diglycol carbonate thermoset, refractive index 1.50 | It has excellent optics and low chromatic aberration, and it is half the weight of glass — the default for a mild prescription. |
| impact-resistant plastic | polycarbonate, index 1.586, or Trivex at 1.53 | Polycarbonate is effectively unbreakable and is required for children's and safety eyewear; Trivex has similar toughness and better optics. |
| high-index plastic | thiourethane materials at index 1.67 or 1.74 | A higher index bends light more per millimetre, so a strong prescription can be made thinner — at the cost of more colour fringing. |
| anti-reflective coating | a stack of metal oxide layers, vacuum-deposited | Each uncoated surface reflects several per cent of light; the stack cancels reflections by interference, improving contrast and night driving. |
| other coatings | hard coat, hydrophobic top layer, photochromic dye layer | Plastic lenses are soft, so the hard coat is what makes them survive a cleaning cloth at all. |
Other medical and personal care objects
- Condom Dipped natural rubber latex, or synthetic polyisoprene or polyurethane for latex allergy — plus silicone lubricant.
- Surgical mask Three layers of polypropylene, of which only the electrostatically charged middle one does the filtering.
- Diaper (nappy) A superabsorbent polymer that holds many times its own weight in fluid, sandwiched between nonwoven plastic layers.
- Contact lens A water-swollen polymer gel — and the whole design problem is getting oxygen through it to the cornea.
- Dental filling Either a mercury-silver amalgam or a light-cured resin packed with glass — and the resin shrinks as it sets.
- Tampon Compressed cotton, rayon or a blend, with a withdrawal cord and either a cardboard or plastic applicator.
- Adhesive bandage (plaster) A plastic or fabric backing with pressure-sensitive adhesive, and a pad faced with a film that will not stick to the wound.
- Artificial hip A titanium or cobalt-chrome stem, a ceramic or metal ball, and a crosslinked polyethylene socket liner that is the wear surface.
- Syringe A polypropylene barrel and plunger with a rubber tip seal, and a stainless steel needle on a standard taper.
Common questions
- What is an Eyeglass lens made of?
- Almost never glass — usually CR-39, polycarbonate or a high-index plastic, under several thin coatings.
- What is the standard plastic of an Eyeglass lens made of?
- CR-39, an allyl diglycol carbonate thermoset, refractive index 1.50. It has excellent optics and low chromatic aberration, and it is half the weight of glass — the default for a mild prescription.
- What is the impact-resistant plastic of an Eyeglass lens made of?
- Polycarbonate, index 1.586, or Trivex at 1.53. Polycarbonate is effectively unbreakable and is required for children's and safety eyewear; Trivex has similar toughness and better optics.
Related pages
- Condom Dipped natural rubber latex, or synthetic polyisoprene or polyurethane for latex allergy — plus silicone lubricant.
- Surgical mask Three layers of polypropylene, of which only the electrostatically charged middle one does the filtering.
- Diaper (nappy) A superabsorbent polymer that holds many times its own weight in fluid, sandwiched between nonwoven plastic layers.
- Contact lens A water-swollen polymer gel — and the whole design problem is getting oxygen through it to the cornea.
- Dental filling Either a mercury-silver amalgam or a light-cured resin packed with glass — and the resin shrinks as it sets.
- Tampon Compressed cotton, rayon or a blend, with a withdrawal cord and either a cardboard or plastic applicator.
- Adhesive bandage (plaster) A plastic or fabric backing with pressure-sensitive adhesive, and a pad faced with a film that will not stick to the wound.
- Artificial hip A titanium or cobalt-chrome stem, a ceramic or metal ball, and a crosslinked polyethylene socket liner that is the wear surface.
- Pencil Stationery and paper
- Tennis ball Sport and games
- Banknote Around the house
- Golf ball Sport and games
- Paper Stationery and paper
- Glass Building materials
Sources
- Official vendor product documentation — At One Place