A shower curtain liner, typically made of polyester or vinyl, is mainly used to keep the water from your tub or shower from leaking to the floor. It’s also used to keep your shower curtain dry and is placed inside the tub. Most shower curtain liners come in plain white or are transparent since they’re not intended for decoration. They can also be used even without a shower curtain. A shower curtain, on the other hand, is mainly used to add privacy to your shower by covering the curtain liner and for aesthetics to enhance the look of your bathroom. They don’t necessarily serve to keep water from leaking to the floor.