I had a compression shirt once, that I used over a binder as a swim shirt. I tried putting it on without the binder once, just to see what it would do, and honestly, it didn't work for me AT ALL. Didn't even sort of flatten, just kind of stretched around my chest. I feel like your chest has to be pretty darn small for one of these shirts to be effective on its own. Unless you're like an a-cup or smaller, I wouldn't waste my money on one if I were you.