보이차 is called puer cha in China, if i Romanized it right. It is an aged tea that is usually sold in compressed disks. You flake off the tea leaves to use them for brewing. IIRC you can buy 3 year, 5 year, and 7 year tea, and the age greatly impacts price. A lot of people in China and Korea drink it because it is believed to be good for diabetics. It is a real tea, but as i understand, it contains no caffeine.