The term R-value can refer to properties of materials such as insulation or soils, a value with no address in computer science, and a kind of measurement in statistical studies. Here we will discuss R-values in relation to insulation.

The R-value is an indicator of thermal resistance used to illustrate the efficiency of insulation. It is the ratio between temperature differences in an insulator and the heat flow through it. If the thickness of the material in meters is 'T' and Thermal Conductivity is 'K', the formula for converting thermal conductivity to an R-value measurement is as follows: = T / K. The answer is a measurement of Kelvin square meters per watt or K*m2/W.

The US Department of Energy has made recommendations on R-values for certain areas of the continental United States based on the climate and local energy costs for heating and cooling. However, it is better for the homeowner to know the case of their own home. In order to calculate the R-value, begin by finding the thermal conductivity of your material (K) on a thermal conductivity table (easily found online). Measure and record the thickness of your material (T). Divide the materials thickness by the conductivity number. Make sure the number for T is expressed in meters. If it isn't, you must convert it. For example, 1 inch is equal to 25.4 millimeters or 0.0254 of a meter.

There are different R-values for different kinds of walls. A Clear Wall R-value is that of a wall with just studs and does not include the framing surrounding windows, doors and corners. A Center of Cavity R-value is an estimate of the cavity space between studs. The Whole Wall R-value is an estimate that includes both the Clear Wall and Center of Cavity R-values attributes. Do not be surprised if it is up to 40% less than a Clear Wall R-value.

When you are calculating the R-value of a space you intend to install insulation in, pay correct attention to weatherization and the quality of vapor barriers. This is especially true with batt and blanket insulation. In harsh weather areas and application in older buildings, the rain and wind can diminish the effectiveness of insulation, especially if there is water infiltration. For example, if you are re-insulating the attic or soffits of an old house, the condition of the roof will affect the life of the insulation, which will in turn reduce your R-value greatly. In addition, if a vapor barrier does not adequately cover the batt insulation, your R-value can be reduced. While some types of insulation are water resistant, the build up of moisture will eventually cause mold to grow and in extreme cases, pooling of water in the walls. Spray foam insulation is a great way to get your R-value nice and high without having to worry about air infiltration and water issues. The nature of the expanding foam means all the little gaps you may not see, but are responsible for cold air entering the house, will be filled in when the foam rises. Polyurethane foam is water resistant, so even if moisture does enter the cavity it will have a very hard time going deeper into your home.

There is some discussion on which methods of insulation have the highest R-value, but it can be a biased conversation. Vacuum insulated panels are considered by some to have the highest R-value and the greatest flexibility as it can be installed directly on top of existing insulation. However, it is also the most expensive form of insulation. Aerogel apparently has the next highest R-value, followed by polyurethane foam which generally has an R-value of 5 or 6. Regular batt insulation has an R-value of 2 or 3. Choose your insulation carefully, based on application, budget, potential R-value and installation. Each part of the equation is important in your choice.