A shower curtain liner is a waterproof or water-resistant sheet that hangs inside a shower or bathtub. Its primary purpose is to prevent water from splashing outside the shower area, helping to keep the bathroom dry and free from mold and mildew. Liners are typically made from materials like vinyl, PEVA, or fabric. These liners come in various sizes, colors, and designs, allowing them to complement the outer shower curtain. Many liners are machine washable or can be easily wiped clean, making maintenance simple. Some liners also feature magnets or weights at the bottom to help them stay in place while showering.