What is Expanding Insulation?

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  • Written By: Koren Allen
  • Edited By: Jay Garcia
  • Last Modified Date: 25 February 2020
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Expanding insulation is a type of liquid foam that is either sprayed or poured into place. Commonly used to insulate home appliances and hot tubs, expanding insulation is becoming more popular in home insulation as well. It has many advantages over traditional fiberglass batts or blown insulation.

Expanding insulation is a combination of liquid polyurethane or acrylic latex, mixed with compressed gases, also called blowing agents. It can be poured into attics or other enclosed cavities, or sprayed onto surfaces that are not enclosed. As the liquid hardens, or cures, the gases expand, causing the foam to grow and fill in the entire cavity, sealing up cracks and crevices as it expands. For this reason, expanding insulation is ideal for odd-shaped areas where traditional insulation batts are difficult to fit.

Expanding insulation usually has a higher R-value than other types of home insulation. In the U.S., all insulation is given an R-value, which is a measurement of thermal resistance. Insulation with a higher R-value provides more effective barriers against heat loss. Expanding insulation is more expensive than other types of insulation, but will save money in lower heating and cooling costs over the life of your home.


Prior to the 1970s, expanding insulation was mixed with CFC gases to produce the expanding effect. Because CFC's are known to damage the Earth’s protective ozone layer, these products are no longer produced in the U.S. Most expanding insulation now uses propane or carbon dioxide as a blowing agent. This results in a slightly decreased R-value, but is safer for the environment.

For large insulation projects, professional installation is usually recommended for several reasons. Some of the gases used as blowing agents are highly flammable until they are cured, but professional installers are experienced in handling these types of risks. Once cured, most spray-foam insulation is flame resistant. Spray foams are messy to install, another good reason to hire a professional. With some quick-expanding foams, the expansion can be so drastic that it causes damage to the framework and structures surrounding the area to be insulated, particularly door and window frames. A slower-expanding variety can help avoid this damage. Experienced installers can advise you on which method is best for your particular structure.

For smaller projects such as sealing up cracks and gaps, expanding insulation is available at your local home store in convenient aerosol cans. Always read and follow the manufacturers label carefully, wear protective clothing, and be careful not to apply too much until you are familiar with how the product behaves.



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Post 1

Building a house in deep South Texas and have spray foam on all the rafters. The installer tells me not to install attic ventilation. is that correct or will I eventually get mold without attic ventilation?

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