Foam boards -- rigid panels of insulation -- can be used to insulate almost any part of your home, from the roof down to the foundation. They are very effective in exterior wall sheathing, interior sheathing for basement walls, and special applications such as attic hatches.

Adding spray foam insulation is one of the most effective ways to make a home more energy-efficient and comfortable. DIYers and pros can spray this insulation between studs, rafters and other spaces, and the formula expands in place to fill in all the tiny spaces that fiberglass batts might not reach.

Made of either open-cell or closed-cell polyurethane (a plastic), or a special cement, this insulation goes on as soft foam or foaming liquid, filling all spaces and then stiffening in place. Applied only by professionals, it’s more costly than other options but it is the best at plugging air leaks.