Several insulation types can work well in the attic, depending on how you plan to use the insulation and your installation budget. Blown-in cellulose or fiberglass makes quick work of insulating and air sealing the attic, but loose insulation is not ideal for finished spaces. Fiberglass batts are easy to install but may be too thick to use under a finished floor. Spray foam can seal and insulate in one step, and it offers high R-values per inch, making it great for finished spaces, but it is a bit more costly than the alternatives.