Dudou, is basically ancient Chinese underwear, or ancient Chinese bra specifically, ancient Chinese children also wear it for warm though. It's written as "肚兜" in both traditional&simplified Chinese characters, and means "belly wrap" literally.

Dudou is basically a rhomboidal piece of cloth which covers the breasts and belly, but leave the back uncovered. It has four attached strings so one can tied at the neck and back to keep it in place. It can be solid or embroidered with different patterns that have different implied meanings. The material could be cotton and silk, rich people also use silver and even gold for the strings.

Different from the modern brassiere, ancient Chinese women wear dudou to flatten the breasts. The reason for that is flat-chested women were thought to be graceful in ancient China. Ancient Chinese also wear it to keep the warm of the belly, and even put some herbs in the layers of it because that was considered salutary. Dudou can have pockets, so people can put small valuable things in them, such as rings and necklaces.

There were different styles of underwear in ancient China, such as xieyi , baofu, xinyi, liangdang, hezi, moxiong, hehuan jin, zhuyao etc., among which dudou is the most famous one(maybe because it's closest to modern times). Dudou first appeared in Ming Dynasty(1368-1644), and still be worn in Qing Dynasty(1944-1912). It fade away after that, and is barely wore by modern Chinese people in the daily life. But some modern Chinese women find it a sexy underwear and have the ancient style meanwhile.

You can wear dudou inside the hanfu , qipao and tang suit.