To understand how home insulation works it helps to understand how heat flows. Heat flow involves three basic mechanisms — conduction, convection, and radiation. Conduction is the way heat moves through materials, like when a spoon placed in a hot cup of coffee and it warms up. Convection is the way heat circulates through liquids and gases. Convection explains why hot air rises and cooler, denser air sinks. Convection presents the largest challenge for properly insulating homes. Radiant heat is the third type of heat flow, it travels in a straight line and heats anything solid in its path that absorbs its energy.
No matter what material it is flowing through, heat flows from the warmer to cooler area until there is no longer a temperature difference. As heat flows it looses energy. So, the more space and material in your home, the more energy is lost in the heating process. In winter, heat flows directly from heated living spaces to adjacent unheated attics, garages, basements, and even to the outdoors. Heat also moves indirectly through interior ceilings, walls and floors — wherever there is a difference in temperature. Without enough home insulation you are paying to melt the snow around your house, instead of simply warming up living spaces.
Home insulation materials work by slowing conductive heat flow and, to a lesser extent, convective heat flow. Radiant barriers and reflective insulation systems work by reducing radiant heat gain. An insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value — the higher the R-value, the greater the insulating effectiveness. The R-value depends on the type of insulation, its thickness, its density and where the insulation is installed.