Because Boosters are designed to work with our protective underwear to increase total absorbency. Unlike pads, they do not have a plastic backing so that liquid can flow through into the underwear below once saturated. They quickly wick moisture away from the skin and are topped with a soft, cotton-like material to keep you dry and comfortable. Boosters should be changed when full but before soaking through which reduces costs; this means the underwear is a backup and need not be replaced as often.
Boosters hold more than 4 cups of liquid and are a great choice when traveling with limited bathroom breaks, or overnight when extra absorption is required. They also reduce costs, as a replacement booster is less expensive than a new pair of underwear.