These are a bit big (not thick but covers a large area).  I use this under a sports bra so I do not look completely flat.  It has fake nipples built in but they are shallow enough that they barely show through the sports bra, and do not show through over a T-shirt.  I wear these sideways (long way horizontal) because they are so long.  Otherwise they will show from the top of the sports bra.  Does not work in a regular bra due to large size.  Maybe this could work if your existing boobs are large or you are a larger frame person (I am a 32A so only works with a sports bra or cami with shelf bra that is cut high).  If you want to use this with a cami with a shelf bra, if the cami isn't cut higher to the neck, these falsies are likely to show.  These are very lightweight foam so if you are going for 'feels real' this might not be what you are looking for...