The term 'KIND OF MATTRESS' can be solved by the crossword solution AIR, which is a three letter word. AIR mattresses are a type of mattress that are filled with AIR and are often used for camping or as a temporary sleeping solution. They are usually made from a durable material such as vinyl or nylon and are inflated using an AIR pump. AIR mattresses are lightweight and easy to transport, making them a popular choice for those who need a portable sleeping solution.