Plus S 2K 13.56MHz RFID Key Tag is made of ABS material with rfid chip and antenna . It will be durable and injection ABS case then sealing rfid chip under ultrasonic machine without any space sideview so that you can use them in out-door harsh environment and waterproof. The Plus is the only mainstream IC compatible with M1K and M4K ,and it uses AES -128 ( advanced Encrption Standard ) for authentication , data integrity and encrption ,besides it available in two versions ,MIFARE® Plus S and MIFARE® Plus X , both versions have 2kB or 4kB EEPROM as optional for you  .It is widely using for public transprtation , access management , electronic toll collection and loyalty programs