Suction and increased blood flow to the nipples can increase sensitivity and improve circulation. The Size Matters See-Tru Nipple Boosters enlarge and stimulate using gentle suction. Simply place them over the nipple and squeeze the bulb to create a mild yet effective vacuum. Once you let go, these fun nipple toys will stay in place on their own. With the see-through chamber, you get to watch all the action as you play!