When you hear the word insulation, the first thing that probably comes to mind is the fluffy pink batts of fiberglass you see lined up in every hardware store or when you peek into old attics. These rolls and batts may even be the first solution you think of when it comes to considering an insulation solution for your home, whether building a new home or replacing old insulation. It’s in your best interest to think again.

Yes, fiberglass is a quick fix for your insulation problem. Yes, it has one of the cheapest upfront material costs . And yes, installing fiberglass batts can even be a relatively simple do-it-yourself project. All of those “advantages” really just equate to short-term convenience. There are many more disadvantages over time that you should be aware of. This begs the question, is the convenience really worth it? What is the true cost of choosing cheap insulation?

First of all, the main purpose of insulating a building is to more efficiently regulate the internal temperature. This is achieved by resisting the infiltration of outside air or preventing the leaking of climate controlled air from inside your home. The measure of an insulating material’s ability to resist this air infiltration is called the resistance value, or r-value. Fiberglass insulation, in all forms, has some of the lowest r-values of the most commonly used insulation types. Take a look at this comparison of r-value by insulation type:

Insulation Type R-Values by Application
Material R-Value/inch
Closed-cell Spray Foam 6.0 – 6.5
Open-cell Spray Foam 3.5 – 3.6
Polyisocyanurate Board (foil-faced) 5.6 – 8.0
Polyurethane Board 5.5 – 6.5
Polystyrene Board 3.8 – 5.0
Blown-in Cellulose (attic) 3.2 – 3.7
Blown-in Cellulose (wall) 3.8 – 3.9
Blown-in Mineral Wool (attic) 3.1 – 4.0
Blown-in Mineral Wool (wall) 3.1 – 4.0
Mineral Wool (batt) 3.1 – 3.4
Blown-in Fiberglass (attic) 2.2 – 4.3
Blown-in Fiberglass (wall) 3.7 – 4.3
Fiberglass (batt) 3.1 – 3.4


There are two reasons why fiberglass insulation along with other batt insulations like mineral wool have such low r-values in comparison to spray foam insulation and even foam board. The first is the structure of the material itself. Fluffy wool or felt slows the transfer of air and temperature through walls and roofs but does not block it completely.

The second and possibly less obvious reason fiberglass and wool insulation has a low r-value is that the lack of precision during installation. In other words, the material is unable to seal off any spaces, gaps, and holes completely. These seemingly minor gaps that are left unsealed play a major part in a home’s energy efficiency loss and make your residential HVAC system work at a higher capacity than it needs to. Not only are they responsible for the loss of energy, but also allow for the infiltration of pests and airborne allergens. The most foolproof solution against these infiltrations is to have spray foam insulation professionally installed. Spray foam expands and fills in every crack, creating an airtight seal within your home and lowering your HVAC system’s workload.

When it comes to the question of whether fiberglass really is cheaper, only doing an upfront cost comparison will cost you more in the long run. The convenience factors of fiberglass, like the lower cost of materials and the ability to install it yourself, are considerably short-sighted when compared to the advantages of newer forms of insulation like closed cell spray foam. Compare fiberglass’ misleading “advantages” to its low r-value, resulting energy loss, and high HVAC workload. These all equate to year-round higher energy bills. Higher bills month after month will quickly chip away at the amount you “saved” by going with a cheap material. In 2-4 years you’ll face a significant loss versus what you would have saved by insulating with advanced materials from the start. The savings on your energy bills by using spray foam insulation, which can easily be calculated, would continue to add up for years to come after the cost gap has closed.

On top of the post-installation financial loss over time, cheap insulation does not have as long of a lifespan when compared to newer approaches like spray foam insulation. It takes about 10 to 20 years on average for fiberglass to settle, collect dust, and harbor pests. After this point, it’s time to replace your insulation yet again. This timeline is dramatically shorter if your fiberglass insulation is exposed to moisture damage before its natural replacement point. Both fiberglass and cellulose insulations retain water, which can quickly lead to the growth of mold within your walls. Closed cell spray foam insulation has an indefinite lifespan and is completely water resistant, so unlike with fiberglass or any insulation material that breaks down and settles, you wouldn’t have to reach out of pocket to replace your insulation again.