Tested on thousands of ears for the optimal fit. Thanks to the latest miniaturization techniques, the electronics have been packed into a new, compact design. Waterproof and sweat-resistant. Ideal for your training. With an IP57 rating, the headphones are completely waterproof and resistant to sweat. Nothing will stop you from running through a storm or sweating for your new personal best at the gym. Are you ready for the longest run of your life? Then recharge your own batteries – because your headphones' battery doesn't need it. This is made possible by smart energy management and a new low-energy Bluetooth 5.0 chip. Ambient noise, only when you want it.