If you don't know much about it, you might be looking at that thin piece of foil-looking material and thinking, how on earth will that insulate my house? There are three ways that heat is transferred, in general: conductive (transfer of heat through solid materials, which heats adjoining solid materials), convective (think of a convective oven - the physical movement of air when it is warmed), and radiant (heat rays moving through air from a warmer space to a cooler space.
Traditional house insulation, either the fiberglass or blow-in kind, provide a barrier for conductive and convective heat transfer.
While not stopping the heat transfer completely, they do slow it down.
If you look at the rooftops of houses about twelve hours after it snows, you'll notice that some houses differ than others regarding how much snow is left.
Houses with poor insulation will have less snow, so a sign of good insulation is indicated by snow that hasn't melted from the house's heat.
However, those sorts of house insulation materials don't do anything for radiant transfer of heat.
As I mentioned before, they only slow down the transfer of heat without stopping it completely.
Imagine a mirror that reflects heat waves rather than light waves.
This is the concept of another kind of insulation that may be referred to in a variety of ways: radiant barrier, foil insulation and bubble insulation, among others.
These are to be used in conjunction with the traditional house insulation, because with the exception of bubble insulation, radiant barriers do not block conductive or convective heat transfer.
Rather, using both types of insulation will enhance the effectiveness of the other, providing the greatest amount of efficiency for heating and cooling your house, because heat neither escapes nor penetrates it.
With origins in the NASA space program, radiant barriers look like aluminum foil, but comprise of a greater amount of aluminum for greater reflectivity.
The reflective material is reinforced with a woven scrim to increase durability.
Radiant barriers generally are fire-resistant and have been known to help reduce the spread of a house fire.
Radiant barriers can be perforated or non-perforated, as well as sandwich a layer or two of bubble-wrap-like bubbles.
Each of the varieties of radiant barriers has a specific use, so consult a professional as to the proper use of each one.