Sunglass Tech Guide

A definitive guide to sunglass and lens terminology

Air Link Temples:

Julbo’s proprietary Air Link Temples reduce bounce while increasing comfort. The arms of the sunglasses have a length of suspended rubber running along the bottom, which acts as a mini shock absorber during activity. 

Alti Arc Mineral Lenses: 

Alti Arc lenses are made of mineral glass and utilized in Julbo’s mountaineering eyewear—they’re the only mineral glass lenses that Julbo offers. They provide excellent scratch resistance and superior optical quality, which sets an industry benchmark for glacier glasses. An external anti-reflective coating improves visual comfort by eliminating stray reflections, and a flash finish improves the filtration of visible light by applying a mirror effect to the lens. Mineral lenses are more fragile than polycarbonate or Trivex lenses and can shatter if dropped. They’re slightly heavier than polycarbonate or Trivex lenses, too. 

Anti-fog Coating:

This permanent coating is applied to the interior of Julbo’s REACTIV Photochromic lenses.It’s chemically bonded to the lens, working on a molecular level to prevent water molecules from bunching together and forming fog. The result is best-in-class fog prevention, no matter the conditions or your effort. When wiping with a microfiber cloth, you may notice the inside of the lens is slightly tacky—this is the anti-fog coating. It won’t rub off, meaning the best way to clean your lenses is with soap and water.

Base Curve: 

All lenses feature a base curve, which is the measurement of how flat or wrapped your sunglasses are. The higher the number, the greater the wrap. The standard base curve of sunglasses is 6, and most sunglasses range from 4 to 10. Most of Julbo’s sunglasses have a base 6 curve, excluding the Montebianco 2 and Monterosa 2 which are a base 8, meaning they have a more wrapped fit. 

CustomFit Temples:

These thin and lightweight temple arms have a metal core that allows them to bend, enabling a customized fit. CustomFit Temples are covered in Grip Tech rubber for a soft and grippy finish. 

Cylindrical Lenses:

Unlike spherical lenses, which curve vertically and laterally, cylindrical lenses curve just laterally. Imagine if the lenses were cut from a cylinder, wrapping side to side. Julbo’s Fury and Density are examples of sunglasses with cylindrical lenses.

Flash Finish:

Lenses with a flash finish are either colored or treated with a colorful mirror treatment that will only be visible from certain angles or at certain light levels. This type of finish is a staple of eyewear and provides a touch of style while filtering light.

Glare Control:

Julbo’s Glare Control lenses are about 80% polarized. This partial polarization eliminates glare off reflective surfaces (such as snow, ice, or water), while allowing for unobstructed viewing of electronics, like a phone screen or boat navigation system. 

High Contrast:

Lenses with a high contrast label have a “warm” base color in the brown/red/rose family. A high contrast lens enhances detail both close up and farther away better than a gray base lens. A high contrast lens is especially good on snow.

Lens Base Color:

This is the color of the lens material when it is initially molded. In general, a gray base color offers a neutral tone with no color enhancement, making it ideal for people who like a standard tint to their sunglasses. Brown, rose, and violet base colors all offer enhancement, which tends to make colors ‘pop,’ increase contrast, or reduce eye fatigue in bright conditions.

There is no “best” base color: The ideal option varies depending on local climate and weather, as well as personal preference, since color perception varies by person.

Lens Category:

Sunglass lenses are rated on a 0-4 scale, and the number corresponds to the visible light transmission (VLT)—the higher the VLT, the lower the category. 

Category 0 is the lightest lens—virtually clear and best for dark conditions. Category 4 is meant for the brightest and highest exposure conditions, and frames with Category 4 lenses include side shields. Most everyday sunglass lenses are Category 3. Julbo’s lenses use this category naming convention. For instance, a REACTIV 0-3 lens will span categories 0-3.

Category VLT

Category 0 80-100% 

Category 1 43-80%

Category 2 18-43%

Category 3 8-18%

Category 4 3-8%

Light Amplifier:

Lenses with the Light Amplifier name brighten your surroundings thanks to their yellow or light orange base. This helps enhance ambient light, making them especially good for use at sunrise/sunset or when traveling in and out of shadows.

MagneFix Interchangeable Lens System:

This exclusive magnetic attachment system, utilized on the Julbo Edge, features a magnet on the bridge of the sunglass frame and lens, allowing for quick and easy lens changes. 

Mirror Coating:

This reflective optical coating applied to the outside of the lenses makes them look like small mirrors. Mirror coatings decrease the amount of light passing through the lens by a 10-60%, making them especially useful in bright conditions. The color of a mirror coating is aesthetic only and does not affect the lens base color or the color the wearer sees. 

Photochromic Lens Technology:

Photochromic lenses adjust to changing light conditions, getting lighter or darker depending on the amount of UV light present. The more UV light, the darker the lens becomes, and vice versa. Photochromic technology is often applied as a chemical laminate to a lens's exterior, but in the case of Julbo’s REACTIV lenses, it is sandwiched into the material, allowing these lenses have the widest photochromic range and fastest reaction time of any photochromic lenses. 


Polarization reduces or eliminates glare, easing eye strain during long days outside and increasing visual contrast, comfort and clarity. It allows light necessary for vision to pass through and blocks reflections that interfere with vision. 

Polarization operates on the same principle as Venetian blinds, filtering light along a single axis. Direct light and reflected light hit your eye along different axes. In sunglasses, the polarization pattern filters light traveling along a horizontal axis, providing the most effective protection from surface glare off water, snow, and windshields.

Julbo’s polarizing treatment comes in two forms: a thin chemical laminate that’s applied to the surface of the lens and a unique chemical laminate that’s sandwiched within the lens. 

The first form—the laminate used with polycarbonate lenses (Polarized Spectron 3)—is lighter and more affordable but can become scratched off over time. The latter form—used in our REACTIV lenses—protects the polarizing film from scratching and, depending on the thickness of the laminate, can provide more glare protection and higher optical quality

Polycarbonate Lens:

First used in sunglasses in the 1980s, polycarbonate lenses are impact resistant, lightweight and UV protective. Thanks to those features, polycarbonate is a popular material for lenses in performance and kid’s sunglasses. Polycarbonate lacks the optical quality of mineral glass or Trivex and is not as durable or scratch resistant as Trivex. It is, however, more scratch resistant and has better optical quality than acetate.

REACTIV Photochromic Technology:

REACTIV photochromic lenses adjust to changing light conditions and provide clear vision for every situation. With the widest range and fastest reaction time on the market, REACTIV technology leads the industry in performance photochromic eyewear.

REACTIV photochromic technology is "baked" into the lens, so it never wears off, which is why Julbo backs all REACTIV lenses with a lifetime warranty. Each lens takes nearly 20 hours to manufacture, and the optical quality is nearly as good as that of glass. 

Spherical Lens Shape: Unlike cylindrical lenses, which curve side to side, spherical lenses curve both laterally and vertically—imagine if the lenses were cut from a sphere and retained that round shape. Julbo’s Rush and Ultimate are examples of sunglasses with spherical lenses.


First developed for use by the military in helicopter windshields and fighter jet windshields, Trivex was tailored for optical lenses in 2002, at which point it became one of the most lightweight and impact-resistant lens materials available. All Julbo REACTIV Photochromic lenses are made from Trivex.

Trivex lenses exceed the FDA minimum impact standard for street/dress eyewear by a factor of 60 times and provide 100 percent protection from the sun's harmful UV rays. The cast molding process used to make Trivex lenses mimics how most other plastic and high-index plastic lenses are made: a liquid monomer is poured into molds and hardened in heated ovens. Unlike the injection molding process used with polycarbonate lenses, this slower cast molding process results in sharper optical quality.

UV Protection:

All Julbo lenses are rated to UV-400 and protect against 100% of UV A, B, and C rays. Ultraviolet light (UV) is present even on cloudy days, and UV protection is extremely important for maintaining eye health.

Visible Light Transmission (VLT):

This refers to the percentage of light that filters through a lens—the higher the number, the more light passes through. A window in a home, for example, might have a VLT of around 70%, allowing most visible light to pass through while filtering enough to keep your sofa from getting bleached. A typical sunglass lens, like a home’s window, has a fixed VLT. The VLT of Julbo’s REACTIV lenses, on the other hand, changes as ambient light changes. Regardless of VLT, Julbo’s sunglasses lenses provide 100% protection from harmful UVA, B, and C light.

3D Nose:

Julbo’s proprietary 3D Nose is a fully adjustable nose bridge. The nosepiece features a metal core that can be bent and will retain its shape for a custom fit; it’s covered in Grip Tech rubber so it will stay put even in the presence of sweat and sunscreen.