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Which Loose Fill Insulation is Best? A Comparison Between Cellulose and Fiberglass


If you are looking at installing insulation or fixing your air sealing, there is no doubt you have heard about 10 different opinions on loose fill insulation and which is ultimately the best. The truth? Most home improvement contractors out there will tout the benefits of the materials which they sell, and their opinions and recommendations are often guided by these purchasing decisions rather than facts. At Windows on Washington, we have installed all different types of insulation materials and always recommend insulation based on scientific research as well as real, quantifiable results we have achieved across the homes of all of our customers. In this article, we will be comparing cellulose and fiberglass loose fill insulation so you can make an informed decision about which insulation is best for your home.

When Should You Choose Cellulose Insulation?

It is important to note that different insulation materials work best in different applications around the home. When it comes to the best insulation for loose fill in attics, however, we recommend borate only stabilized cellulose. Why? There are several reasons we at WoW believe borate stabilized cellulose is best, such as:

  • Superior performance. The R-value of borate stabilized cellulose is much higher compared to loose fiberglass filled insulation.
  • Cellulose is made from recycled materials, making it the more eco-friendly choice.
  • In terms of pests, borates are one of the most effective insecticides for your home.
  • Dissimilarly to other insulation, borate stabilized cellulose does not contain VOC (volatile organic compounds) content and does not offset gas like ammonium sulfate stabilized cellulose or formaldehyde containing fiberglass does.

The downside to using borate stabilized cellulose? It is often more expensive than fiberglass loose fill insulation.

When Should You Choose Fiberglass Insulation?

On the other hand, many industry experts suggest loose fill fiberglass insulation, this is currently dominating the construction housing market. However, as many homeowners may know, builders are currently under enormous pressure to produce a beautiful new home, but at the same time cut costs and stay within a certain budget. If you are considering fiberglass insulation, here are some things you should be aware of.

  • Fiberglass insulation is more cost effective than cellulose insulation.
  • Fiberglass insulation does not effectively protect your home from insects or pests.
  • For many people, fiberglass can be a skin and lung irritant.

Perhaps the biggest concern when it comes to fiberglass insulation, however, is that it is subject to convective air movement, which means it results in a large degradation of the cumulative R-Value. What does this mean in basic terms? Essentially, it means while you as a homeowner have paid for the Energy Star recommended R-49 in your attic, the real environmental performance of loose fill fiberglass is more like R-25 or less when you need it most.

Why WoW Chooses Cellulose Insulation

At Windows on Washington, we are saddened by the amount of times we have customers come to us with attics that have been overblown with fiberglass, reporting little to no change in the temperature difference and overall comfort in their home. The real reason fiberglass insulation is so popular? At the end of the day, it comes down to its cost, and not due to its superior performance. At WoW, we believe insulation options should be chosen on real life performance, and not what is cheapest or what is most popular. That is why Windows on Washington chooses borate only cellulose for all of our loose fill insulation projects. Correctly installed cellulose insulation in conjunction with targeted air sealing will ultimately increase the comfort of your home, and drastically reduce your utility bills.

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Topics: Insulation, Spring