Insulation retards heat journeying from warm to cooler surfaces or spaces. In the winter, when warm room air exits through walls, rises up through the attic and roof, and flows down through the floor, insulation blocks--or at least slows--its departure. And in the summer, when warm outdoor temperatures try to force their way into your air-conditioned rooms, insulation holds the heat at bay. By slowing heat movement, insulation not only saves energy but reduces drafts, making a house more comfortable. Some types--foam in particular--seal out air infiltration, a major contributor to heat loss.
