The solar-powered Adidas RPT-02 SOLs are a great choice for outdoors enthusiasts and eco-minded folks who'll enjoy a long-lasting charge just by being exposed to the sun. They also sound great, but if active noise cancelation is top of your list, you should look elsewhere.

At first, the Adidas RPT-02 SOL headphones sound too good to be true: Self-charging Bluetooth headphones powered by...light? Give me a break.

But they're real and they're pretty incredible. And they're a surprising solution to a very familiar pain point.

We've all been there: You head out the door in a rush and realize you'll be riding the subway in silence because you forgot to charge your headphones. Or mid-run with four miles to go, your playlist suddenly stops because, again, you forgot to charge your earbuds. SOLs make those kinds of groan-inducing annoyances a thing of the past. They're lightweight, durable, and, according to Adidas, they won't need to be charged (or replaced) for years.

But why would Adidas, a publicly-traded company, be interested in decreasing the number of purchases consumers make of their products?

"Being a conscious brand is not just about the number of pieces you sell," says Adidas product manager Anders Olsson. "It's also about creating a longterm relationship with the customer. If they can really see that your product will last over time, they will come back again and again. All brands should focus on prolonging lifetime and finding materials that are good for the planet, because otherwise, we will end up nowhere."

Olsson said that the team behind the headphones focused on two main elements of sustainability: making the SOLs physically durable and using recycled materials to produce them. 

"We recently made a lifecycle study of a headphone and if we double the lifetime from two to four years, we have a huge reduction in CO2 emissions," he said.

Basically, durability equals sustainability, and as a result, the SOLs are light, stylish, and solid. I've dropped them and walked in the rain with them on, and they still look and sound great. They're IPX4-rated, meaning they're splash proof, and the removable ear pieces and headband covers are washable, with replacements available for purchase online should they ever tear. The design team nixed a hinging earpiece, which Olsson said is the most commonly broken part of a headphone, opting instead for a modular design that breaks down easily for recycling. 

Olsson said the team also focused on sourcing materials with "the lowest possible co2 emissions." 87% of the plastic in the SOL is post-consumer recycled plastics, which Olsson said is not that much more expensive to produce than new plastic. Recycled nylon has also been incorporated into the fabric that covers the earpieces and headband. The plastic making up the other 13% of the headphones is new and was used for parts that require greater durability.

The band of the headphones is made of a printable solar panel — a Swedish technology called Powerfoyle — that transforms all types of light into power. Leaps in technology have enabled the cost of printing a solar panel, the amount of energy that solar panel can produce, and the amount of energy needed to power headphones to converge into a consumer-friendly application. You can see that tech at work as the headphones communicate with the Adidas Headphones app to measures light in milliamps in real time. It's impressively responsive, reacting nearly immediately to changes in light.

At full charge, Adidas says the headphones provide 80 hours of playtime. But most people who use the SOLs on walks or in the gym won't ever need to charge them. The headphones don't even come with a charger (though if you really feel you need one, you can request one from Adidas for free). In other words, you should have infinite play time simply by wearing them out during the day, or placing them on a windowsill.

I've been using my SOL headphones on and off for about three weeks, and the battery usually hovers at 45% and has never dipped below 38%. Even while walking outside on a rainy, cloudy day, the headphones gained about as much power as they lost.

While I'm not wearing them, I put them on a dresser that gets indirect light. The headband has a three-ring indicator to show when the headphones are facing the strongest light possible for the best charge. Simply tap the button below the rings on the left earpiece and they will glow: one for weakest light, three for strongest.

Though my headphones never lost power, they didn't charge as quickly as I expected in environments with good or great light. But I am also used to plugging a device into a wall socket and watching it juice up to 100% in a matter of minutes or hours. The SOLs don't work that way, but they still work.

Music sounds great on the SOLs. They're not noise-canceling, but the squeeze of the band creates an on-ear seal that has a slight, pleasant dampening effect. This enhanced my focus without blocking out environmental sounds, like barking dogs or approaching cars. Call quality was excellent as I wore the SOLs while running errands and they didn't pick up the kind of random street noises that my AirPods magnify.

If you're someone who wants to completely block out the world while working out, the SOLs aren't for you. But they're pretty darn great for everyone else.

To control power, pairing, and playback, the SOLs rely on single, square-shaped knob, which is surprisingly responsive.

To ensure the SOLs could be comfortably worn on your head throughout an entire workout, the team behind them had to tweak compression and fit so they stayed put without squeezing too hard. They reasoned that if you could complete a burpee — i.e, a jump into the air followed by a swift drop into a plank — without the headphones falling off, the SOLs would withstand most workouts.

Impressively, you can, though I did find myself pushing the headband back into place every once in a while as I exercised. The headphones offer a snug fit and the earpieces can be adjusted higher or lower on your head with a firm push the your preferred direction.

I personally found the SOL headphones to be comfortable to wear for about an hour to 90 minutes, after which my ears would start to ache. That mostly has to do the combination of band pressure and the earpieces' nylon weave, which is made to withstand wear and wick sweat as you work out. But it's a little rough on the skin. Olsson said that the weave would soften and get more comfortable in time, both with use and after being tossed in the washing machine (always on cold).

A 90-minute time limit is perfectly fine by me since I rarely work out for longer than that, but if you're hoping to use these out the gate for distance runs or long sessions at the gym, look elsewhere.

The SOLs are impressive. They sound great, are easy to use, and, most importantly, they don't add stress to an already busy day. When I wanted to go on a walk, I could just grab them and go, without worrying if they had enough charge to get me back home. They're sturdy but light, as well as stylish but functional. At $229, the SOLs are in high-end headphone territory, so they're a bit of an investment. But at least they won't need to be replaced any time soon and almost never need to be charged.

Plus, they help to ensure a greener future which, in the end, is priceless.