Insulation comes in a variety of shapes, sizes, materials, and prices. Use the least expensive kind that does the job, and then pay more for special features like moisture resistance or higher R-value. Fiberglass blankets are commonly found in walls, attics, and floors. They are easy to cut and install, but are susceptible to air leaks. Loose fill fiberglass and cellulose fiber are good insulation for flat ceilings. Unless, however, the homeowner has experienced with these products, they do require professional installation. When installing fiberglass blankets, loose fill fiberglass, and cellulose fiber, protective gear is required. Extruded polystyrene boards are used primarily over walls and foundations. They are resistant to air and vapor penetration and have a higher R-value, but are relatively expensive.