Refers to the curvature of the lens, which in part determines how deeply the frame will wrap. Petrol sunglasses come in 6, 8 and 9-base styles. A 6-base style has a flatter curvature more similar to an ophthalmic or prescription eyeglass frame. 8 and 9 base styles wrap more deeply around the sides of your face, providing greater protection from light 'leaking' into the sides of the frame.

A good sunlens will prevent harmful light and glare from reaching your eyes, but certain frames shapes will allow some light to 'leak' into the top and sides of the sunglass frame, circumventing the lens. this light can bounce off the inside of the lens surface and produce fatigue-inducing glare. Petrol styles featuring Repelium™ have a multilayer anti-reflective coating applied to the inside of the lens, which helps minimize this form of glare while not interfering with the lens color of light transmission levels.

The transparent front part of the eye that covers the iris and pupil, the cornea is succeptible to UV light damage. All Petrol sunlenses filter out this harmful light, preventing it reaching your corneas.

In a metal eyewear frame, the soldered metal loop that holds the lens securly in place, often held firmly closed by a rimlock screw near the hinge.

A trademarked product of EMS-GRIVORY Corporation, TR-90 is a plastic polymer commonly used in the creation of sport and other impact-resistant eyewear frames. It is lightweight, resistant to stress cracking and material fatigue, and stands up well against UV exposure and extreme temperatures. TR-90 frames are injection molded and then painted in wide range of colors. A well-made Grilamid frame can rival a handmade zyl frame in richness of color and finish, while providing the more sport-oriented benefits of the TR-90 material.

What are polarized sunglasses? Polarized lenses contain a thin sheet of polarizing film that helps reduce the harsh glare of light reflecting off flat surfaces. These lenses can be cast individually, or cut from a large sheet of lens/polar film/lens and then thermoformed or bent to produce the lens curvature. Not surprisingly, bent sheet polarization has greater levels of distortion than individually molded, injected polarized lenses. With injected polarized, the precision-cut polar film is introduced in the lens mold, producing superior optical performance.

Eliminate prismatic distortion by shifting the optical 'sweet spot' of each lens from the geometric center (or mid-point of the lens) to the optical center directly in front of the eye.

Polyvinyl chloride, commonly abbreviated PVC, is a widely used thermoplastic polymer. Petrol uses this material for the nosepads on its metal eyewear frames as it has great slip resistance than silicone, another material frequently used in the manufacture of eyewear nosepads.

Most Petrol styles feature Repelium, a cutting-edge lens coating that's smudge-resistant, moisture-repellent, oil and sun lotion repellent, and provides the highest level of scratch resistance available in any plastic sun lens. Repelium also includes a premium anti-reflective treatment applied on the inside of each lens that obliterates bounce-back glare and disturbing reflections inside your sunglasses. With Repelium, fogging dissipates. Water beads and rolls off. Fingerprints disappear. All while maintaining razor-sharp clarity, color recognition and light transmission levels.

The retina is a light sensitive part inside the inner layer of the eye. Comparable to the film inside a camera, the retina is vital to communicating visual images to the brain via the optic nerve. A growing amount of medical research has implicated high energy blue light (part of the visible light spectrum) as a source of damage to the retina. Petrol sunlenses absorb significant amounts of blue light, preventing it from reaching your retinas.

Frames designated as "Rx-Friendly" have lens sizes and shapes most-suitable for conversion to prescription sunglasses. Generally frames with a base curvature higher than 8 and toric lens shapes are more difficult to convert to prescription eyewear. Furthermore, the frame design itself might dictate whether a prescription lens can substituted.

A hinge that flexes slightly beyond a fully open position and then springs back, helping maintain the shape of the eyewear frame over time and offering a very comfortable fit.

Smooth-functioning closure that allows your sunglasses to close flat, but stops the temple tip from striking the inside of the lens.

A lens with different horizontal and vertical base curvatures, producing a unique look in deep-wrap frame styles while maintaining optically correct, distortion-free vision.

Ultraviolet light (UV) comes naturally from the sun. The three commonly referred to categories of UV are based on wavelength:

  • UVA (320-400 nanometer wavelengths) is linked to tanning, skin aging, eye damage. 

  • UVB (280-320 nanomenter wavelengths) is obstructed by the earth's ozone, but increasing damage to our ozone is allowing more UVB radiation to reach us. UVB causes sunburns, snow blindness, and can damage your skin and eyes.

  • UVC (100-280 nanometer wavelengths) is highly obstructed by the ozone, so lower levels of UVC radiation reaching the earth's surface.

All Petrol lenses offer UV absorption up to 400 nanometers, which blocks 100% of all harmful UVA, UVB and UVC rays from reaching your eyes.

The application of lens coatings in a vacuum chamber results in an even, flawless application of the coating material.

A light-responsive feature that automatically adjusts the darkness of your lenses to surrounding light conditions. Unlike ordinary light-transitioning photochromic lenses that react only to ultraviolet light, Petrol VisoChromatic lenses react to both UV and visible light, offering the perfect level of glare-cutting light transmission—even when behind the UV-coated windshield of your car. VisoChromatic lenses adapt quickly and feature the longest-lasting photochomic pigments available anywhere.

Clearness of vision, or the ability of the eye to resolve detail in distant objects.

Zyl is a plastic material commonly used in the manufacture of ophthalmic quality frames. Zyl can be produced in a vast range of colors, and 'sandwiching' two or more layers of zyl together (a process called lamination) adds even greater richness and color to the frame style. Zyl is hand-cut from large sheets and polished to a natural sheen rather than painted. It is heat molded to produce the proper curvature for the frame and holds it shape well. Most zyl frame temples have metal reinforcements or core wires embedded inside for strength and great ability to custom fit the frame.