A twin-size mattress is a type of mattress that measures 38 inches wide by 75 inches long. It is designed to fit a standard twin bed frame and is commonly used in children's rooms, guest rooms, and small spaces. This size is ideal for single sleepers, providing enough space for comfort without taking up too much room. Twin-size mattresses come in various materials, including memory foam, innerspring, and latex. They are often available in different firmness levels to cater to individual sleep preferences. Due to their compact size, twin mattresses are also popular for bunk beds and daybeds.