Bikini tops designed to move with you shouldn't sag and bag when wet. But even the best bikini tops and tankini tops can loosen slightly in the water. That's why your bikini, tankini, or one piece swimsuit should fit with a snug, almost compressive fit on dry land, without any big bulges or spillovers. Every T9 bra-sized swimsuit has a style-specific sizing guide, so you can dial in your fit, but if you're looking for more general tips on finding the perfect size swimsuits for you, check out our swim fit guide.