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Lens materials comparison

CR-39, Trivex, polycarbonate, 1.60, 1.67 and 1.74 side by side, with a quick thickness comparison.

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Lens materials compared

Index, Abbe value, weight and impact notes for six common spectacle lens materials. Values vary slightly by manufacturer.

Bar chart of refractive index for each material Taller bars mean a higher index, which makes a thinner lens for the same prescription. Refractive index: higher = thinner lens CR-39 Trivex Poly 1.60 1.67 1.74
Tap a button below the chart to compare a different property.
MaterialIndexAbbeSpecific gravity
CR-39standard plastic (1.50) 1.4981.498–1.499 5857–58 1.321.31–1.32
TrivexPPG Trivex (1.53) 1.5301.527–1.532 4543–45 1.111.11
Polycarbonate"poly" (1.59) 1.5861.586 3028–31 1.201.20–1.22
1.60 high indexe.g. Mitsui MR-8 1.6001.59–1.60 4136–42 1.301.30–1.36
1.67 high indexe.g. Mitsui MR-7, MR-10 1.6701.66–1.67 3231–32 1.361.35–1.40
1.74 high indexe.g. Mitsui MR-174 1.7401.73–1.74 3332–33 1.471.40–1.47

Impact and practical notes

  • CR-39

    Impact: Passes the FDA drop-ball test at normal thickness (about 2 mm thick in the center), but it can crack. Not the first choice for children, sports, safety glasses or drilled rimless frames.

    Clearest optics of the plastics and low cost; thicker in stronger prescriptions.

  • Trivex

    Impact: Very high impact resistance (a high-impact safety material). Excellent for drilled rimless frames, children and sports.

    Lightest common lens material. Blocks UV. Clearer optics than polycarbonate, a little thicker.

  • Polycarbonate

    Impact: Very high impact resistance. The usual choice for children, sports, safety glasses and people with sight in only one eye.

    Thin and light, blocks UV. Low Abbe value: color fringes toward the edge in stronger prescriptions. Scratches easily without a hard coat.

  • 1.60 high index

    Impact: Good impact resistance for everyday glasses (passes the FDA drop-ball test). MR-8 is often used in drilled rimless frames.

    Thinner than CR-39 with good optics (MR-8 has an Abbe value of 41). Values vary most between brands.

  • 1.67 high index

    Impact: Good impact resistance for everyday glasses (passes the FDA drop-ball test). Not a safety lens unless certified as one.

    Noticeably thinner for strong prescriptions. Lower Abbe value; an anti-reflective coating is strongly advised.

  • 1.74 high index

    Impact: Lower impact resistance than the other plastics here (Mitsui rates it "OK"); generally not recommended for drilled rimless frames.

    Thinnest plastic lens, but the heaviest per cubic centimeter. For very strong prescriptions; add an anti-reflective coating.

Compare two materials (same prescription and frame)

Words used here
Refractive index
How strongly a material bends light. Higher index needs flatter curves for the same power, so the lens is thinner.
Abbe value
How little a material splits white light into colors. Higher is clearer; low Abbe can show color fringes when looking through the edge of a strong lens.
Specific gravity
Density compared with water (grams per cubic centimeter). Lower is lighter for the same amount of material.
Drop-ball test
US FDA rule: every dress eyewear lens must survive a 5/8-inch steel ball dropped from 50 inches. Safety eyewear (ANSI Z87.1) is a higher standard.

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Reading the numbers

  • Refractive index: higher index bends light more, so the lens needs flatter curves and is thinner.
  • Abbe value: higher means less color splitting (chromatic aberration). Polycarbonate (about 30) is the lowest here; CR-39 (58) the highest.
  • Specific gravity: the density of the material. Trivex (1.11) is the lightest; 1.74 is the densest, but its thinness can still make a strong lens lighter overall.

Values vary slightly by manufacturer and by the reference wavelength (US charts use the helium d line; Mitsui and many European sources use the e line, which reads a little higher). Check the lens maker's data sheet for a specific product.

References

Calculators are study aids. Always verify finished eyewear with your instruments and follow your practice's procedures. More optical calculators.

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