I ordered a medium to scared a small would be to small. Nope, I needed a small. The back at the top is like elastic so it stretches some. The material is soft. Not super thin. Not see through. I will order another one but a size small instead. The "V" in the middle, because my size is to big the bottom of the "V" pokes out some. That's the only down fall of getting the size up. I'm not sure if bra size helps at all but I wear a 36B and weigh 139 so a small works better.