How to Insulate Walls With Foam

Updated February 21, 2017

A new and innovative type of insulation makes it easy to insulate finished walls. Expanding foam insulation can be easily added into a wall that has existing insulation. Foam insulation expands evenly throughout the inside of the wall around old insulation, wall studs and electrical or plumbing fittings. The insulation is pumped into the wall by inserting a fill tube through drilled holes. As it expands, the foam insulation fills every corner and crack to create a solid wall of protection. Expanding foam insulation kits are found at most home improvement stores for home use.

Read the manufacturer's instructions and recommendations for setting up the kit equipment and to get a thorough understanding of the process and application of slow rise expanding insulation before starting your project.

Use a stud finder to locate the wall studs. Mark the location of the studs on the wall with a piece of painters tape. Drill all holes between the wall studs. Make the holes large enough for the fill tube to be inserted effortlessly into the wall. Drill the holes at the three- and six-foot level, then eight inches from the ceiling.

Consult the manufacturer's instructions for how much foam to use and how long it will take to fill a wall. Use a plastic straw to detect the level of the foam inside the wall by inserting the straw in the hole above the hole you are filling. When the foam reaches the hole above, take the fill hose out of the lower hole and move it to the next hole up. Continue testing the foam level and moving the hose upward until the wall is completely insulated.

Use a foam saw or a putty knife to scrap off the excess foam that oozed out of the fill holes once it has hardened.

Use a putty knife and joint compound to fill the holes. Let the compound dry thoroughly before lightly sanding it to a smooth surface. Repeat if necessary. Texture the wall if necessary to match existing walls and paint.


Fill the walls slowly and allow time for the foam to expand before adding additional foam to avoid overfilling the wall. Loose or separating drywall can be reinforced with a drill and drywall screws.


Slow rise foam is recommended for existing walls to avoid filling the walls too fast and causing breakages and drywall damage. Wear protective clothing, safety glasses, rubber gloves and a protective mask when working with foam insulation. Keep kids and pets away from the work area.

Things You'll Need

  • Safety glasses
  • Rubber gloves
  • Protective mask
  • Slow rise foam insulation kit
  • Painters tape
  • Stud finder
  • Drill
  • Plastic straws
  • Foam saw
  • Joint compound
  • Putty knife
  • Sandpaper
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About the Author

Wendy Adams has been a Web designer, content writer and blogger since 1998. Her love for writing began in high school and continued with a life of personal writing, content writing, blogging, commentary and short articles. Her work appears on Demand Studios, Text Broker, Associated Content and on client websites and numerous social network sites.