Bluetooth earbuds designed for working out are a pretty personal peripheral – they go in your ear and they mingle with your sweat – so finding one that works just right and can also stand up to some abuse is tough. We tried out Sol Republic's latest effort at cracking the code, its Relays Sport Wireless in-ear headphones, and have this review.

Let's just get right to the bad news: we tested these out primarily by taking them for a few trail runs and they didn't stay in our ears. We tried all the replaceable ear tips and even some that we've had luck with from other earbuds, and one side would always eventually work itself loose. The tip design employed on the Relays just isn't as good for repetitive jarring motions when compared to larger ear gels and different shapes like those used on Bose Freestyle earbuds or the more novel Revols.

But for workouts in the gym or on a bike, the Relays worked pretty well. They are as lightweight and comfortable in the ear as any Bluetooth earbud we've tried. Two modules are located along the main cable running between the right and left buds. Those modules house the microphone for calls and control buttons on one side, and the battery and USB charging port on the other. They're designed to rest on your neck, and an adjustable slide can also be used to tighten or loosen the unit behind your head.

One nifty little feature of the Relays is that they have indoor and outdoor listening modes. Basically the outdoor mode provides a bass boost to compensate for low range booms that might otherwise be lost in the ambient din.

We were also fans of the quick charging capability that allows you to get an hour of music from just 10 minutes of charging and 8 total hours per charge. Most Bluetooth headsets charge up quickly already, but we'll take any improvement we can get in this area.

The Relays are rated IPX4 to stand up to sweat and splashing, and we found they stood up to sweaty, swampy conditions below the hairline just fine.

The only thing that really bothered us about these earbuds was the fit, which unfortunately is the one thing that matters the most. Lightweight is great, but we'd rather have the added weight of an over-the-ear design if it keeps our music in our ears.

Sol Republic launched by selling an initial batch of wireless Relays for $74.99 via an Indiegogo campaign that has already sold out. However, due to delays in production, many of those orders have been late to arrive and Sol Republic has begun issuing refunds. Keep an eye on Sol Republic's website and Amazon store in the coming weeks for more units to become available.

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