I wear a 34DD and I know that is a bit out of the way of a c/d cup but honestly this was made for a C cup -- if that.
This covered barely any of my boobs AT ALL.

The silicone is very thick so I would imagine if fitting that it would give you a very big boost.. the equivalent of adding a full cup size.

I had bought this to line my bathing suite which is rather on the small side... a D cup- which is why I thought that If I bought this my actual size and the size of these triangles wouldnt matter. I was looking to cover the space in a suit that measures a 34D. It did not even come close and so I was unable to wear them. I had tried to slip them in the given spots in my suit and they were three sizes too small. unless this fits perfectly in your bathing suit than you will be able to see the edges if your suit is thin.