Pure cotton. One more thing is very important. If you are still developing in adolescence, you must buy the right size+plastic. For those over 22 years old, buy a more tolerant one. It's okay to be bigger. As for the influence of bra on health, it is true. Too tight is really healthy. But that kind of unhealthy risk mostly happens to adult women, especially married women, so it is better to be tolerant of bras in adulthood and wear less at home ~
Pure cotton is the best material. Don't buy thick ones. Sweating is easy to breed bacteria, and it is not easy to wash and is not conducive to shaping.
According to your bust, go to the store and they will tell you what bust you are and what bra type you are suitable for. But usually the kind of "seamless chest shaping" is the best, and most people are very suitable for it ~!