I have to disagree with previous reviewers-- I wear a 34DD, and this works great under low cut shirts, and it's not at all uncomfortably tight. I am definitely not "supermodel thin." I wear a size L or XL in shirts, and this fits fine. I'm probably ordering another one soon.

Update: I recently got remeasured professionally at the bust, and my size is the same as I thought above-- 34DD, so I'm not really sure why other reviewers of the same size are having such a different experience with this product. I also ordered another one of these, and it also fits just fine.