Several years ago, most insulation material was either mineral wool or fiber glass. These materials have similar insulating properties, and it became common practice to specify insulation in terms of inches of thickness. Today, many different insulations are on the market, and each has its own characteristics. Insulate where heat flows Heat flows from warm to cold areas. Insulation should be placed where you are trying to slow the heat flow.
Obvious places are in all exterior walls and the ceiling immediately below the attic area.
Remember to insulate walls between heated and unheated rooms such as a garage, basement, or storage room. When energy costs were low and supplies were plentiful, floor insulation generally was not recommended because heat loss through the floor helped keep the basement area warm and comfortable. This is still a good idea if the basement is used frequently. If it is used only occasionally, you save fuel dollars by heating it only when you use it. Therefore, not much is lost through the floor.