The term 'Little Pig Building Material' is a reference to the classic fairy tale, 'The Three Little Pigs'. In the story, the first pig builds his house out of STRAW, which is a five-letter word that is the solution to this crossword. STRAW is a material made from dried stalks of grain plants such as wheat, oats, and barley, and is commonly used for building insulation, animal bedding, and craft projects.