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What is Insulation?

Updated: Jan 21, 2021

Seems like an obvious answer to most, but there can be more to it than what most people think. This post is going to bring you through some of the basics of insulation, kind of like "Insulation 101".


How does insulation work?

To really understand how insulation works, it helps to understand heat flow. Heat flow involves three basic mechanisms, radiation, conduction, and convection.

Radiation or radiant heat, travels in a straight line and heats objects that absorb energy. Radiant heat is said to heat objects not the air, which is kind of true, but as it heats the objects they in turn heat the air. Radiant heat is a great option for large areas, like barns and pole buildings. It heats the area quickly and typically more affordably when the area is not always heated.

Conduction heat is the way the heat moves through objects, the reason you don't leave a spoon in the pan of boiling water. You may think that since the handle of the spoon wouldn't be hot because it wasn't directly in the water, thanks to conduction the heat has traveled up the handle and is now hot enough to burn your hand.

Convection heat is the way the heat circulates through liquids and gases. Convection is why warmer air rises and cooler air sinks.

I will touch more on heat and different ways to use different kinds of heat and furnaces in a later post.


What is "R-Value"?

As I said in the introduction, this is going to be "Insulation 101", in order to completely understand "R-value" we would need to go really deep into math and science. This is going to be the simple answer. "R-value" is a rating system used to grade insulation products and materials insulating properties. "R" is the absolute thermal resistance, the greater the

"R-value", the greater the resistance. The equation below is how the "R-value" is calculated, in case there are some of you reading this that want to calculate "R-values" of objects around the house.


More materials than insulation have an "R-value", although not as much as the insulation. For example, the OSB plywood on the exterior of a house is R-0.51 for 7/16", R-0.74 for 1/2", and the sub floor which is typically 3/4" is R-0.91. The drywall or sheet rock on the interior walls is calculated at R-0.45 for 1/2". So, as you see all these materials help with insulation, but not as much as the next few products we will get into.


What types of insulation products are available?

There are many different insulation products available. Listed below are a few of the more popular materials used. All of the "R-values" of the products will be calculated for a 2x4 wall.

Fiberglass- A lot of you have probably seen the cotton candy looking materials in walls, and many of you have probably felt the burning itch after handling it. This product has been around for many, many years. It used to be the go-to insulation for any and all buildings that were going to be heated and/or cooled. It is still widely used in many structures and applications, and is the most cost effective way to get a structure insulated. That being said, the efficiency of fiberglass insulation is the lowest compared to it's counterparts. Fiberglass insulation is most effective when there is something behind it to block air movement, like when applied against a concrete wall. That is why you often see fiberglass insulation with a paper applied to one side, also known as "kraft faced fiberglass".

-Fiberglass insulation is calculated at R-13.





Faced fiberglass insulation.















Un-faced fiberglass insulation.



Blown and Sprayed Cellulose Insulation- Blown cellulose is typically used in attics, it is a loose pack insulation which is good for applications where nothing is going to be covering it. Sprayed cellulose is a tightly packed insulation which is applied wet to make it denser and fill a cavity that is going to be covered over with something like drywall. It is much denser than fiberglass which allows less air to pass through, or less convection heat loss.

-Blown cellulose at 15" deep is calculated at R-49.

-Sprayed cellulose in a 2x4 wall is calculated at R-13.



Blown cellulose in an attic.

















Sprayed cellulose in a stud wall.















Closed cell foam- Closed cell foam is made up of individual cells, which are completely closed. The cells are pressed together so that air and moisture are unable to get inside the foam. Closed cell foam is a very rigid and hard surface once completely cured. This makes the structure very strong when the walls are sprayed with this material. Closed cell foam also acts as a vapor barrier to keep the home air tight.

Closed cell foam is calculated at R-20.


Closed cell foam being sprayed in a new home.










Above- When the closed cell foam is sprayed, it expands, foaming out past the studs. After it has cured for a bit, the insulator then goes and cuts the excess off, flush with the studs.


Open cell foam- Open cell foam is made up of individual cells, much like closed cell foam. The difference between the two, you probably guessed by now, is that open cell foam cells are not completely encapsulated, or closed. This gives the product a much softer and more flexible finish.

Open cell foam is calculated at R-13.


Open cell foam-

- Less dense.

- Spongy.

- Absorbs and holds moisture.

- No structural strength.





Hybrid insulation- This is when you spray 1" of closed cell in the cavity against the ply wood, and fill the remainder of the space with sprayed cellulose. This gives a structural advantage, vapor barrier, and also doesn't have the price tag of doing the whole area with closed cell foam. It is kind of the best of both worlds.

Hybrid insulation is calculated at R-16.

Story time- (sorry, this is instead of a picture.) A few years ago, I did a "mother in law suite" that was about 1,000 square foot. The addition was located on the west side of the house, which was open to a farmer's field and located towards the top of a hill. The wind there can be quite extreme, especially during the winter months. The budget was fairly tight, so we couldn't do complete closed cell foam. I recommended that they do the "hybrid" option, and explained what it was and how it worked. We still talk on occasion, and every time we do she brags about how it is quiet and warm in her new area and the rest of the house you can hear the wind constantly. It was a very effective and budget friendly option for her and she is very happy that she went with it.


I hope that this gave you a little bit of insight on your options when it comes to insulation. In the future I would like to write a post on different exterior products that can help with the "R-value" in a home as well. I always like it when people understand their options and can make an educated decision.

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