This product is specially designed to match the shape of your head. Therefore it will feel comfortable and stay in place while doing sports. With its fashionable appearance and built-in MP3 player with HiFi earphones (sound output up till 85dB ), you can always enjoy high-quality music. When the built-in Lithium battery fully charged, it can play music for about 2- 4 hours. it also supports micro SD card functions up to 32Gb plugged into an inbuilt TF port.