A tight-fitting sports bra may flatten or compress your breasts temporarily, but that also helps keep them out of the way and restrict movement. However, some sports bras are not designed to flatten, but are shaped more like regular bras and actually encase and support each individual breast. “The secret to a good sports bra is compression and encapsulation,” says Burke. “Encapsulated cups offer support and separation, one boob per cup, and will help each breast stay where it’s supposed to be.”