Poly and Trivex Lenses: Facts and Fiction
Even though Trivex has been available for years and polycarbonate for decades, there is still much debate, confusion and even long-held myths about how Trivex and polycarbonate stack up against one another in the world of lens materials. We'll lay out the facts, in the video below, put the lenses to the test, and attempt to put the question to rest.
Of course which ever your choose, both Trivex and polycarbonate lenses can be ordered in the style of your choice from your favorite independent optical lab.
Polycarbonate
Born from the space race in the 1960's and introduced to the ophthalmic lens market in the late 1970's, polycarbonate has been around the block a few times and enjoys a sizeable market share, particularly in children's and safety eyewear due to its superior impact resistance. With a higher index of refraction and lower specific gravity, polycarbonate lenses are thinner and lighter than their plastic and glass counterparts. Inherent UV protection and wide product availability also contribute to its popularity.
One of the chief complaints about polycarbonate is its optical quality or lack thereof. With an Abbe value of 29, polycarbonate's chromatic aberration is the highest of any lens material in use today. Furthermore, some dispensers are hesitant to use polycarbonate in drill-mount frames because of its lack of tensile strength and likelihood of cracking around drill holes. We suggest putting the material through your own tests and deciding for yourself.
Trivex
Introduced in 2001 by PPG, as the only lens material other than polycarbonate to pass FDA Impact Resistance Test (@ 1mm CT), the High Velocity Impact Test, and meet ANSI Z87.1 '89 standards, Trivex has been slowly increasing in both popularity and availability. While Trivex has a slightly lower refractive index (1.53 compared to 1.58), it's specific gravity, 1.11g/cm3, makes it the lightest of any lens material available today. Like polycarbonate, Trivex also has inherent UV protection. However, unlike polycarbonate, Trivex has an Abbe value of 45, making it optically superior on paper. The tensile strength of Trivex makes it highly resistant to cracking around drill holes. In fact, Younger Optics guarantees its Trivex products (Trilogy) for life, against stress fractures and drill mount cracking.
Weight Comparison
Despite Trivex's lower specific gravity, the weight difference between Trivex and polycarbonate lenses is negligible in practical scenarios. The tests showed a mere half-gram difference between the two, suggesting that in everyday use, this weight variance is hardly noticeable.
Chemical Resistance
A key factor in lens durability is resistance to chemicals like acetone. The experiment showed that while Trivex remained unaffected by acetone, polycarbonate lenses showed some degradation. However, in typical usage where lenses are not extensively exposed to harsh chemicals, this may not be a significant issue.
Optical Clarity and Abbe Value
Trivex, with a higher Abbe value, theoretically offers better optical clarity and less chromatic aberration than polycarbonate. The tests somewhat reflected this, with Trivex displaying less color dispersion at the lens periphery, indicating clearer optics.
Tensile Strength
The tensile strength test surprisingly revealed that Trivex broke under less strain than polycarbonate. This result challenges the common belief that Trivex is always stronger or equal in strength to polycarbonate, especially when considering coatings that can alter the material properties.
Heat Resistance
Testing for heat resistance simulated conditions like leaving glasses in a hot car. Both materials showed significant deformation at high temperatures, but neither cracked nor showed structural weakness at the insertion point, indicating good resilience.
UV Protection
Both materials are rated highly for UV protection. However, polycarbonate showed a slight UV penetration (3%), whereas Trivex blocked 100% UV rays. This difference, while minimal, might influence decisions for those seeking maximum UV protection.
Tintability
Contrary to popular belief, the ability to tint lenses depends largely on the coating rather than the material itself. The tests showed varying results in tinting capabilities, with some polycarbonate lenses tinting more effectively than Trivex.
Price and Availability
Trivex tends to be more expensive and less available than polycarbonate. The variety of options in polycarbonate surpasses that of Trivex, offering more choices in clear, AR-coated, and polarized lenses.
Impact Resistance
A crucial aspect of lens material comparison is impact resistance. The tests conducted presented some surprising results in this regard. While both polycarbonate and Trivex are often touted for its strength, the experiments showed that its resistance to impact varies depending on the coatings applied. For instance, a Trivex lens shattered when struck by a pellet, whereas a polycarbonate lens withstood the impact better. Conversely, in another test using a hammer, a polycarbonate lens shattered, which was unexpected given its reputation for high impact resistance. These results suggest that the coatings on the lenses play a significant role in their overall impact resistance. It was found that coatings could reduce the strength of the lenses by a significant margin.
This finding underscores the importance of understanding not just the base material, but also the coatings applied to it. The impact resistance of both Trivex and polycarbonate can be significantly altered by the addition of scratch-resistant or anti-reflective coatings. Therefore, when choosing a lens material for its impact-resistant qualities, it's crucial to consider the type and quality of coatings used.
In summary, the impact resistance test revealed that neither Trivex nor polycarbonate could be universally deemed superior in all circumstances. The performance of each material under impact depends on various factors, including the manufacturing process and the coatings applied. This information underscores that in-general, opticians should refrain from discussing impact resistance unless in the context of safety glasses.
Conclusion
Trivex has the impact resistance and inherent UV protection of polycarbonate. With a lower index of refraction, Trivex may be slightly thicker than polycarbonate, but is negligibly lighter, and can be surfaced to the same 1mm center thickness. Trivex rises above polycarbonate with both its optical quality and suitability for drill mounting in theory. But as our video showed, real-world tests may yield different results.
A couple of key points we discovered in our testing is first of all, when you're dealing with average prescriptions, the differences in the material performance are often negligible, also keep in mind that when any type of coating is added, all bets are off in terms of impact resistance.
Finally, when comparing the price of Trivex to polycarbonate, make sure you are comparing apples to apples. If you are looking at a spherical polycarbonate product, compare it to a spherical Trivex product. You'll likely find the difference to be less than you might think. But generally speaking polycarbonate is going to be significantly cheaper and be available in more options.
The tests conducted in a real-world (unscientific) setting reveal that both Trivex and polycarbonate have their unique strengths and weaknesses. Factors such as weight, chemical resistance, optical clarity, strength, heat resistance, UV protection, tintability, price, and availability vary between the two materials. The choice between Trivex and polycarbonate should be informed by the specific requirements of the wearer, keeping in mind that coatings can significantly alter the properties of the lens material. As with any optical material, it’s crucial to understand the characteristics and limitations of both Trivex and polycarbonate to make an informed decision.
For more information on other lens material options see: How to Choose the Right Lens Material