Judging by the look, which is a lot like mine, I think it's mostly fat, but it could be gland also.
In my own case I can feel small lumps, but they are hard to find, but I suspect there might be some enlarged strands of gland. It feels like it's mostly fat but I can find like some sort of harder strand-like tissue also. In any case, I think most of the look comes from fat. I suspect that with more gland it would more like "puffy nipples" or something.