Flat chest and thin, you can wear a bra with a sponge. Just choose the size that suits you. Try not to wear half-cup underwear, but wear full-cup underwear. The tightness is just right, close-fitting but not tight, and the fabric is comfortable. The key is good air permeability. Some girls think that flat-chested and thin bodies can be worn without underwear, but this is not the case. If you don't wear underwear for a long time, your chest will sag, which is extremely unfavorable to your breasts.