The Best Expanding Foam to Seal Cracks and Gaps

Insulate the attic, create an attractive water feature, or prevent noisy pipes, all with the help of expanding foam.

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The Best Expanding Foam

Photo: amazon.com

Expanding foam is a flexible product with a wide range of applications including waterproofing, fireproofing, and insulating to reduce the flow of heat into and out of the house. It can also be used for blocking sounds, securing water pipes so they don’t rattle in the wooden frame, sealing cracks and gaps around windows and doors, and more.

The versatility of expanding foam makes it simple to choose a general-purpose product for a variety of applications. However, for more specific uses, like building a pond in the backyard or preventing rodents from entering your home, the expanding foam should be made and tested with waterproofing or rodent blocking in mind. The list of top products below is a great place to start the search for the best expanding foam for your home.

  1. BEST OVERALL: Great Stuff 99108824 Smart Dispenser Gaps & Cracks
  2. RUNNER-UP: DAP 7565000043 Touch ‘n Foam 4001031212 MaxFill
  3. BEST BANG FOR THE BUCK: Great Stuff 282047 Big Gap Filler, 12 oz. (Pack of 8)
  4. BEST WATERPROOF: Red Devil 090806 Foam & Fill Large Gaps & Cracks
  5. BEST PEST-BLOCKING: Tomcat Rodent Block Expanding Foam Barrier
  6. BEST FIRE-RESISTANT: Great Stuff 99112831 Smart Dispenser Fireblock
The Best Expanding Foam Option

Photo: amazon.com

What to Consider When Choosing the Best Expanding Foam

When shopping for an expanding foam for sealing cracks and gaps around windows, insulating moving boxes, or securing wires or plumbing, factor in the expansion size, the functionality of the specific product, and whether it’s applied with a spray can or a handheld gun.

High vs. Low Expansion 

Expanding foam products fall into two broad categories based on the amount that they can expand beyond the liquid size.

  • High expansion foam is typically used in commercial and industrial settings for quickly filling large gaps and cracks in doorways and windows. It is also regularly used for filling holes in the foundation and mortar where water, gas, and electrical lines have been run. This type of expanding foam can expand up to 200 to 300 times its liquid size. It can include open-cell foam, which can allow moisture to flow through the foam, and closed-cell foam, which completely blocks moisture and airflow.
  • Low expansion foam, in contrast, can only expand up to 20 to 30 times its liquid size. This smaller size makes low expansion foam a great choice for home repairs because the gaps, cracks, and utility holes are generally much smaller. High expansion foam would quickly seep out, creating a dripping mess, while the low expansion foam is much easier to manage.

Functionality

Most of the many uses for expanding foam fall into four categories, including waterproofing, fireproofing, acoustic insulating, and thermal insulating.

  • Waterproofing with expanding foam is a common usage around the home. Sealing cracks and gaps in the foundation, walls, and around windows and doors helps prevent water from leaking into the home. Some expanding foam products can even be used to help create ponds, fountains, and other water features for the yard.
  • Fireproofing the home is very important, and some expanding foam products, designed to be highly fire resistant, can be used for this purpose. The foam can seal holes between floors where wires and pipes run and can be used to seal gaps around wall outlet boxes to prevent loosening, while at the same time serving as a fire barrier should disaster strike.
  • Acoustic insulating helps prevent the transfer of noise between rooms, floors, and exterior walls. High expansion foam can be used to insulate a wall, floor, or ceiling, while low expansion foam is used for sealing cracks and gaps where ductwork, plumbing, and electrical run through the home so sound cannot pass through these holes.
  • Thermal insulating is often done with high expansion foam because it can be used to quickly insulate an entire room. However, sealing up cracks around window and door frames with low expansion foam is also important to ensure that the home is properly insulated.

Application

Expanding foam products will typically come prepared for use in a spray can or in separate components that need to be applied with a handheld gun.

  • Spray cans are easy to use. The can comes premixed so there is no wait time before the expanding foam can be applied. These products may also come with a long, narrow dispenser that connects to the nozzle, allowing the foam to be injected into very small gaps with precise accuracy. However, only low expansion foam comes in a spray can format.
  • Handheld guns take more knowledge and experience to use with precision but are the best option for large projects like insulating the attic. These products typically include two separated components in pressurized tanks. The handheld gun has two hoses and connects to both tanks. When the user is ready, the tank valves are opened, allowing the expanding foam to be sprayed through the nozzle of the gun. This type of application is usually only used with high expansion foam.

Our Top Picks

Product efficacy and overall value were the main criteria for assembling this list of the best expanding foam products with a further emphasis on the important shopping considerations mentioned above.

Best Overall

The Best Expanding Foam Options: Great Stuff 99108824 Smart Dispenser Gaps & Cracks
Photo: amazon.com

This expanding foam has a drip-free straw dispenser for precision control and application; the flow of the foam is controlled by a trigger on the dispenser, allowing the user to stop the flow immediately by releasing the trigger. The low expansion foam adheres to wood, metal, and masonry so it can seal gaps, crevices, and cracks inside and outside of the home.

This Great Stuff expanding foam can fill gaps up to 1 inch in width, making it a good choice for installing new windows or doors. The foam dries to the touch in about 15 minutes and can be trimmed after 1 hour; however, it takes about 24 hours before it’s fully cured. After trimming the foam, sand it down, and paint or stain it to make it almost unnoticeable.

Runner-Up

The Best Expanding Foam Options: DAP 7565000043 Touch 'n Foam 4001031212 MaxFill
Photo: amazon.com

Apply DAP Touch ‘n Foam expanding foam to the inside or outside of the home in order to insulate against drafts and moisture accumulation. The expanding foam is resistant to extreme temperature changes, rain, sleet, and snow but is vulnerable to UV radiation, which will discolor the foam. The 12-ounce can of foam comes with a precision straw applicator, making it easy to spray the foam into narrow gaps and crevices.

This fire-resistant expanding foam fills gaps greater than 1 inch in width, creating an airtight, water-resistant seal. It dries in 15 minutes; when it fully cures in 24 hours, it can be sanded, painted, or stained. The low expansion foam repels insects and other pests, protecting the home from infestations.

Best Bang For The Buck

The Best Expanding Foam Options: Great Stuff 282047 Big Gap Filler, 12 oz. (Pack of 8)
Photo: amazon.com

The Great Stuff Big Gap Filler can fill gaps, cracks, and crevices up to 3 inches thick, making it ideal for fixing holes in walls, creating packing for moving boxes, and sealing water, gas, and electric service penetrations. This inexpensive value pack comes with eight ready-to-use spray cans of expanding foam, making it a great choice for large home renovations or multiple projects.

The low expansion foam dries to the touch in just 15 minutes and can be trimmed after one hour. It adheres to wood, drywall, metal, masonry, glass, and most plastics, forming a water-resistant seal once it has cured. The foam takes about 24 hours to fully cure, at which point it can be sanded, painted, or stained.

Best Waterproof

The Best Expanding Foam Options: Red Devil 090806 Foam & Fill Large Gaps & Cracks
Photo: amazon.com

This expanding foam is best used to waterproof the home against the elements. It comes in a ready-to-use can and has a precision applicator straw that makes it easy to fill cracks and crevices in the foundation from the inside of the home or the outside. The barrier created by the foam becomes waterproof and airtight after it has fully cured, helping to seal out moisture.

The low expansion foam can be applied to painted or unpainted wood, concrete, cinder blocks, aluminum, fiberglass, and masonry materials like brick and mortar. It can also be used to seal windows and doors as well as any service penetrations for water, gas, or electricity. It takes about 24 hours to fully cure; after this period of time, it can be sanded, painted, or stained.

Best Pest-Blocking

The Best Expanding Foam Options: Tomcat Rodent Block Expanding Foam Barrier
Photo: amazon.com

Expanding foam is great for preventing water damage and sealing drafty windows and doors, but many products are susceptible to rodent nibbling. Tomcat Rodent Block Expanding Foam Barrier is specifically made to handle mice, rats, and other pests with a dense, bitter-tasting formula that not only seals but also repels mice, instead of becoming a snack.

The low expansion foam comes in a 12-ounce spray can and has an applicator straw so it can be precisely controlled and applied to narrow cracks and crevices. It forms an airtight and water-resistant bond with most building materials, allowing it to be used indoors or out. Once the expanding foam has fully cured, it can be trimmed, sanded, or painted to get a finished appearance.

Best Fire-Resistant

The Best Expanding Foam Options: Great Stuff 99112831 Smart Dispenser Fireblock
Photo: amazon.com

Use this low expansion foam in areas that pose a fire risk, like around outlet boxes or to secure electrical wires. The fire-resistant formula is made to seal service penetrations in the framework of the home so fire and smoke cannot move freely through these gaps. The simple act of blocking off these gaps can prevent a house fire from destroying the entire home. This expanding foam can also create an airtight, water-resistant seal for acoustic and thermal insulation.

Its bright orange color makes this expanding foam easy to identify, and it adheres to most building materials, sealing and insulating gaps up to 1 inch in size. It comes with a long straw dispenser for better control and precise application. It dries to the touch in just 15 minutes; however, it takes a full hour until it can be trimmed or sanded.

Tips on Using Expanding Foam

Expanding foam expands. That may seem like an obvious statement, but it’s something that can be all too easy to forget while spraying the foam into a deep cavity or recess. If the foam is sprayed too quickly, the crevice or gap can overflow, leaving a dripping mess that must be removed with a utility knife after it dries.

Similarly, any accidental spills or sprays on nearby walls should be cleaned up after the expanding foam dries. Trying to clean up an expanding liquid inevitably creates a larger mess that is more difficult to remove. When the foam sets, it can usually be scraped from a nonporous surface, though wood and other porous materials may need to be refinished.

Always inspect the area where the insulation will be applied before installation. Older homes and homes with wooden shingles may be built with a design that allows the natural evaporation of excess moisture. Insulation installed in these areas acts as a sponge, soaking up the moisture instead of allowing it to dissipate. As moisture builds up, mold can grow and eventually rot out the wood.

  • Take time to slowly install the foam in order to avoid overflow.
  • Don’t try to wipe up spills and mistakes; wait until the foam has dried to scrape it off.
  • Carefully inspect older homes before installing insulation to ensure it won’t cause moisture accumulation, which can lead to mold and rot.

FAQs About Expanding Foam

Expanding foam products are designed to seal cracks and gaps, secure plumbing and wiring, and block rodents and other pests from entering the home. Take a look below to find the answers to some of the most commonly asked questions about how to use expanding foam and the dangers it can pose.

Q. Which expanding foam expands the most?

High expansion foam expands the most. It’s capable of expanding 200 to 300 times the liquid size, while low expansion foam can only expand up to 30 times its liquid size.

Q. Is there a waterproof expanding foam?

Yes, some expanding foam is designed to be waterproof. Certain products are even made specifically for building ponds, fountains, and other outdoor water features.

Q. Where should you not use an expanding foam?

Expanding foam isn’t a good idea for every area of the house. Avoid spraying expanding foam too close to electrical boxes or light boxes where the foam can pose a fire hazard, unless it is specifically designed for this purpose. Also avoid using open-cell spray foam on the roof because it can cause moisture to accumulate, rotting out the roofing. If you aren’t sure whether to use expanding foam for a specific problem or in a specific area, check with the manufacturer before using it.

Q. What are the dangers of expanding foam?

Expanding foam needs to be applied with proper ventilation and breathing protection because the chemicals produced by the spray foam vapor can cause asthma, eye irritation, itching, and rashes.