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What is Expanding Foam?

Mary McMahon
Updated May 17, 2024
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Expanding foam is a product which is designed to expand and harden upon contact with the air. It classically comes in canisters with spray nozzles, making it easy to apply the foam in a wide variety of situations. There are a number of uses for this product, with most hardware suppliers stocking several types which can be utilized in many different applications. Most companies clearly list suggested and recommended uses on their products on the packaging, although some consumers may think outside the box when it comes to ways to using this material.

Classically, this product is stored under high pressure. When a user activates the spray nozzle, the pressurized contents spurt out, and they start to expand. As the contents expand, they develop a foamy appearance and they start to harden. This foam can grow exponentially in size, which means that people need to be careful when they use it so that they do not apply too much. Latex, polyurethane, and a variety of other materials can serve as a base for this product, and waterproof, fire resistant, and other specialty versions are available.

In construction, expanding foam can be used as insulation, since foam has some excellent insulating qualities. It may also be used to seal holes, with expanding home sealant also being useful for minor repairs. It can be used around door and window frames to create a tight seal, and it can also be used to plug holes used by insects and animals. Some types can also be used as an adhesive, with several companies making foam adhesive.

People also use this material to make casts of various objects. A small amount of expanding foam can be inserted into a cast and allowed to expand, creating a replica of an object. Prop masters in film and television often use it for this purpose to create lightweight, inexpensive props which can be finished to look like more solid objects. The tendency to conform around a mold or object also makes this material useful for customized product packaging, with shippers making expanding foam packaging to protect delicate items in transit.

A specialized type of expanding foam is used in fire suppression, especially with chemical fires. The foam is designed to quickly fill a room or location, preventing oxygen from reaching the fire and quickly controlling it. Some fire suppression systems are designed to emit expanding foam in a fire, and firemen can also use foam tankers and portable foam canisters to quickly apply foam to a fire.

AboutMechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon188179 — On Jun 20, 2011

By far, this may be a prudent decision only for large-scale jobs as you will receive lots of foam and you have to apply it immediately. That's why spray type is recommended for the majority of DIY projects.

In order to work with this kind of foam, first read the manual carefully. After this, clean the area and put on some old clothes, since removing foam from it may be almost impossible. Use rubber gloves as well. A real advantage of the expanding foam is in the permission to be used in dump environments as well, so you may apply it in, for example, your bathroom.

By anon135709 — On Dec 20, 2010

i need to buy cavity insulation foam to fill the cavity of a semi but have been quoted silly prices making individual cans more economical. Surely this cannot be right.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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