The process of air sealing fills unintentional cracks and holes that allow outside air to enter a home or conditioned air to exit a home uncontrollably. Sealing these leaks can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment. Insulation only works when air is not moving through or around it. So it’s very important to seal air leaks before installing insulation to ensure that you get the best performance from the insulation. Sealing and insulating a home’s “envelope” or “shell”—its outer walls, ceiling, windows, doors, and floors—is often the most cost-effective way to reduce energy bills and improve comfort.