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First, a confession: I don’t usually like wearing sunglasses while running. And I run a lot. I test and review sunglasses for �����ԹϺ���, but most sunglasses kind of suck for running. They fog when you get sweaty, or they jostle around, or they’re too heavy and overbuilt. Many lenses—even the ones billed as transition lenses—are too dark for trail running through dimly-lit forests or on early-morning missions with fickle light (which is when I tend to get my miles in).

So, for years now, I’ve run without eye protection. But on longer runs or mid-day outings in bright sun, I’ve started to notice serious eye fatigue. My legs are holding up fine at mile 20, but my eyes are cooked, which makes seeing trippable hazards in the trail even harder. All of which led me on an exhaustive hunt to find the perfect running sunglasses. I tested a whopping 51 pairs of sunglasses over the last nine months (perk of the job!) and I ended up finding the unicorn I was looking for: the Julbo Density.

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Julbo Density Sunglasses

Bottom line: These sporty, barely-there shield sunglasses excel in changing light, thanks to a lens that adjusts on the fly. You can wear them for a wide range of activities and light conditions.

Pros and Cons
⊕ One of the most lightweight, minimal sunglasses we tested
⊕ Expansive field of view and absolutely no fogging
⊕ Comfortable fit, stays put
⊗ Not as durable as other glasses; frame could snap if tossed around

Lens: Comes with either Julbo’s adaptable photochromic lens, called Reactiv, or a non-photochromic, less expensive option called Spectron.
Frame shape: Shield
Fit: Large
Weight: 20g

To help me test sunglasses, I gathered a team of Lake Tahoe, California-based multi-sport athletes, who were tasked with wearing a variety of shades while doing every outdoor pursuit they could think of. Afterward, they filled out extensive feedback forms with their input. You can see the sunglasses that rose above the rest in our complete review.

I wasn’t alone in my love of the Julbo Density. Some testers even argued over who got to wear the shades on their next testing outing. “These were a contentious pair of glasses in our house,” said Jessica Hamilton, who tested alongside her husband, Goran. “They were used every day of the two weeks we had them.”

Between 13 testers and across three seasons, we took the Density out Nordic skiing, backcountry skiing, hiking, mountain biking and road cycling, climbing 14ers, playing soccer, and biking to pick up our kids from school—but it was trail running where they really shined. In part, that’s because of the lightweight, understated design. “You hardly know you’re wearing them,” one tester said. Another added, “The frame and lens shape were great for keeping out the wind. Mostly, I was impressed with how light they are.”

Thin rubber temples glide over your ears with ease and stay put, while a streamlined frame just along the top of the lens cuts down on bulk. The lack of frame along the bottom of the glasses also made them great for looking down while navigating technical terrain: There’s nothing to obstruct your view.

Breezy ventilation and a big field of view come naturally with this lens shape and size. There wasn’t even a hint of fog inside the lens, even wearing a hat and hood during high aerobic output activities. It’s definitely an oversized lens—it worked best on our testers with larger faces. If you have a smaller head, you might be better off choosing the , which has similar lens tech and style but in a more petite shape.

The Density comes with lens options. You can spend less and get Julbo’s perfectly-good Spectron, a versatile polycarbonate lens that’s durable but doesn’t adapt to changing light conditions. Or you can spend about $80 more for Julbo’s photochromic Reactiv lens, a worthy splurge if you plan to use these in variable light conditions (which is pretty much everywhere, no?).

Forgive me while I gush a little over this lens. It is what sealed the Julbo Density as my top, and only, choice for trail running. Julbo’s Reactiv transition lens technology has a solid reputation amongst cyclists, but until this test, my running friends and I hadn’t discovered this beauty yet. The lens tints darker as you move into brighter light and clearer if you’re in a dimmer place. With road or trail running, the light is always changing, and the lens usually keeps up. Since running is slower than biking or skiing, it allows even more time for the lens to transition. “The shift in tint doesn’t quite adjust fast enough on speedy downhills to make as much of a difference, but it made a big difference on slower uphills,” one tester said.

On low-light days on forested singletrack, the lens was never too dark—no need to lift the shades onto your head; the lens just transitioned to a clearer tint. “Incredible transition precision with clarity in harsh sun and flat light,” said one tester. “I’m super impressed.”

The Density is definitely a sporty look. You might as well have a sign on your forehead that says, “I crush miles.” One tester wrote, “They’re a bit too much of a vibe for the casual outing.” But for endurance athletes—especially runners—looking for a trusty new pair of shades with impeccable optics, this is it.