The age old battle: spray foam vs. fiberglass. Why should I choose spray foam insulation over fiberglass or cellulose?
As a spray foam insulation contractor, this is the number one question I get from potential customers. It's a very important question to ask, being that it's YOUR hard earned money that you will be investing. Like with any investment, you want to know WHAT your investing in and WHY it is a better investment than the latter.
Insulation is a very important investment, mainly because it's a once in a lifetime decision. You only insulate once. The purpose of this article is to help you realize that choosing spray foam as your insulation of choice is the better investment.
Now, being a spray foam guy, I might be a little bias. BUT I too asked this question. Long before I began in the spray foam business, I was a customer. I was deciding whether to spray foam or fiberglass one of my out buildings on the farm (a 40x80 shop). I did my research, asked questions and eventually decided that spray foam was the best for me. To this day I'm glad I went that route.
Now that I am a contractor, I want to share with you my knowledge and research to help save you the time and trouble in your decision to choose spray foam. Lets start by discussing the number one factor when comparing spray foam and fiberglass insulation - R-Value.
The higher the R-Value, the better the insulation, Right?
This is a question that I get quite often. Actually, more often than not it's "Why the hell are you recommending 3 inch spray foam that's only R-21 when I can get R-60 of blown in fiberglass, are you crazy?", Fair question, no matter which way you ask it. Naturally, its safe to assume that a higher number means its got to be better! Right? But is it In the case of spray foam vs. fiberglass?
In order to make the case for the what-seems-to-be measly R-21 spray foam vs. the what-seems-to-be the mighty R-60 fiberglass, I will explain what R-Value is and why it is important to understand the differences in these insulation materials.
R-Value
noun. the capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power.
Alright, so the official definition of R-Value clearly states that "The higher the R-value, the greater the insulating power.". So that R-60 fiberglass is looking like a clear winner. Case closed, right? Not so fast. A key word also in the definition, is "an insulating material." Spray foam and fiberglass are completely different materials, so comparing the R-Value against one-another is like comparing apples to oranges. Let's dive a little deeper in the matter and learn how these materials differ.
Now knowing what R-Value is, lets look at how spray foam and fiberglass compare in the ability to resist heat flow (thermal resistance). The Second Law of Thermodynamics states that heat always flows toward cold. Heat is transferred towards cold either by:
Conduction - The transfer of heat through materials that touch each other, such as a skillet on top of a stove.
Convection - The transfer of heat through liquids and gases. An example of convection is a stove that warms the air around your food.
Radiation - The movement of heat from any source, warming objections around it. One example is the heat emitted from a campfire.
Fiberglass and cellulose insulation work to prevent conduction. However, warm air is constantly flowing through the fiberglass towards the colder surface via convection. So basically the thicker the fiberglass, the more you slow down heat transfer. This results in a higher R-Value.
Spray Foam, unlike fiberglass. doesn't allow air to pass though it. This air tight seal is an extremely important game changer. Unlike fiberglass, spray foam is working to stop conduction and convection. Heat is lost much quicker through convection, or air movement, than it is though conduction. Because of this, it is way more important to have an air tight seal than it is to have conductive resistance. This is why a way lesser R-Value of spray foam achieves better energy efficiency of a much higher R-Value rating of fiberglass.
Remember, you loose more heat through air movement (convection). Spray foam prevents this, whereas fiberglass does not.
To be continued...
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