The term 'breathable stuff' can be broken down into two crossword solutions: AIR (3 letters) and MESH (4 letters). AIR is a mixture of gases, primarily nitrogen and oxygen, that surrounds the Earth and is necessary for life. MESH is a material made of connected strands of metal, plastic, or fabric, which is often used to make clothing and other items that need to be breathable. Together, AIR and MESH create breathable stuff, which is any material that allows AIR to pass through it.