The Boston Globe Installing insulation is the cheapest way to make a house comfortable at the least cost. And, the rule continues, vapor barriers should face the heated part of the house, not the outdoors.
Much insulation has a paper backing.
This is the vapor barrier. A vapor barrier stops the loss of air from the house to the outdoors, therefore saving heat and making the insulation much more effective. It also keeps water vapor from escaping. On the attic floor, put in backed insulation, with the paper facing down. For a basement ceiling, just the opposite.