Pillow stuff is a term used to describe the material used to fill pillows. The most common type of pillow stuff is FOAM, which is a four-letter word that can be found in crossword puzzles. FOAM is a lightweight material made from polyurethane or other synthetic materials that is often used for cushioning and insulation. It is also used in furniture, mattresses, and bedding. FOAM is a popular choice for pillow stuffing because it is comfortable, durable, and easy to clean.