Insulating Ducts: A Guide to Thickness and R-Value

When insulating ducts, understanding the meaning and impact of R-Values and insulation thicknesses is essential to getting the most efficient, affordable outcome on your heating installation project.

The ratings provide a guide for homeowners that determines the effectiveness of the insulation, making it easier to choose the right insulation for your home. Proper insulation can save homeowners time and money, while conserving energy for a greener future.

Understanding R-Values

R-values represent the heat resistant properties of an insulating material. The higher this value is, the better you can expect the insulation to perform.

Ducting values are determined by two factors: the mass of the insulation, consisting of both its density and thickness, and the compression ratio at installation, which determines the final compressed density and effectiveness of the insulation.

Higher compression levels do the opposite of higher R-values. Compressing materials leaves them with less space to occupy and insulate, making them less effective.

The most effective type of insulation is one that is thick, dense, and allowed to take up space, giving it more room to create a barrier between the ducts and the outside air.

Much like an insulating thermos, duct insulation with a good r-value will create a barrier between different air temperatures to prevent the unwanted heating or cooling of conditioned air.

Recommendations for Different Types of Ducting

For home heating applications, one of two types of duct insulation are usually used: blanket duct rap, or insulated flexible duct. Blanket duct wrap is applied separately from the actual ducting process, whereas insulated flexible duct comes with the insulation already wrapped.

Both types of insulation are available in a variety of thicknesses and R-ratings. For most applications, a rating of R-6 or better will provide the best efficiency and long term cost effectiveness.

Purchasing the ducting and the insulation separately is often more cost-effective, and has a greater variety of options when it comes time to choose the r-value of your insulation.


Understanding densities is an important part of working with R-values. Densities fall into one of three categories: low, medium, and high. High density insulation achieves the highest R-value for any given thickness. Be careful not to take these ratings at face value.

It's necessary to factor in compression when determining the efficacy. The amount of compression exerted on duct insulation in most home applications reduces the effectiveness of duct insulation by fifteen to twenty percent.

Ensure Overall Efficiency

In order for duct insulation to properly do its job and reduce your heating or cooling bill, the ducts themselves must be airtight and properly sealed at any joints. Proper maintenance of ducting will increase the efficiency at a very low cost.

Furnace and AC system maintenance is another important factor in the efficiency of your heating and cooling system. Reduce compression in insulation projects wherever possible to get the best mileage out of your duct insulation.