What is the difference between expanding foam and spray foam?

Expanding foam and spray foam are both polyurethane foam products used for insulation and sealing gaps and cracks in buildings. Though they share some similarities, there are important differences between the two that affect how and where they can be used.

What is Expanding Foam?

Expanding foam, also known as one-component foam, is a polyurethane foam sold in pressurized cans. It is typically used by consumers and contractors for small insulation projects and sealing jobs. When the can is opened, the foam mixture reacts with moisture in the air, causing it to expand and harden into a solid foam plastic. The foam expands 30-100 times its original volume as it hardens. Once cured, expanding foam is a durable, lightweight and semi-rigid plastic.

Here are some key facts about expanding foam:

• Sold in pressurized cans that are ready to use
• Expands and hardens rapidly, curing in under an hour
• Comes in low expansion and high expansion formulas
• Used for small gaps and cracks, up to 3 inches wide
• Forms a permanent, airtight and waterproof bond
• Common brands include Great Stuff, Touch ‘n Foam, DAP Kwik Foam

Expanding foam has a more limited range than spray foam when it comes to insulation applications. It is designed primarily for small DIY sealing jobs, filling gaps and cracks around windows, ductwork, pipes and electrical openings. It can also be used as a temporary insulation solution for unusual gaps that are difficult to fill with traditional insulation. The small particle size of expanding foam allows it to compress into gaps and build up to completely fill the space. When cured, expanding foam adds insulating value to the filled cavities.

What is Spray Foam?

Spray foam is a two-component polyurethane foam that requires special equipment to be installed properly. The two components, typically referred to as Side A and Side B, are kept separate until applied with a spray gun. When combined and sprayed, the chemicals react very quickly to expand 30-100 times the liquid volume and harden into rigid cellular plastic. Professional applicators use specialized spray foam rigs to meter, heat, mix and spray the foam into place.

Here are some key facts about spray foam:

• Applied by professional installers using specialized spray equipment
• Two-component formulas require precise chemical metering and mixing
• Highly expanding foam cures in minutes and forms a permanent seal
• Can fill larger voids, gaps and holes up to inches wide
• Excellent adhesion to most construction materials
• Common brands include Demilec, Icynene and Lapolla

Spray foam excels at providing a seamless seal and robust insulation value when installed properly. It is the product of choice for large insulation jobs in new construction and remodeling projects. The largest use of spray foam is insulating roof assemblies, interior wall cavities, crawl spaces, rim joists, attics and foundations. It provides thermal insulation, air sealing and moisture control in one application.

Key Differences

While expanding foam and spray foam are both types of polyurethane foam used for insulation and air sealing, they have distinct differences in their properties, applications and installation. Here are some of the main differences between the two products:

Application Method

Expanding foam comes ready to use in pressurized cans and is applied by consumers or contractors. Spray foam requires special spray equipment and training and can only be installed by professional applicators.

Foam Expansion

Expanding foam expands less than spray foam, with 30-100 times expansion compared to 200-300 times for spray foam. The higher expansion of spray foam allows it to push past obstructions and fill larger gaps.

Foam Density

Expanding foam has a lower density at around 0.5-1.0 pounds per cubic foot. Spray foam has a density of 1.5-2.5 lbs/ft3, giving it higher R-value insulating performance per inch.

Gap Filling Ability

Expanding foam is suitable for gaps up to 3 inches wide. Spray foam can fill spaces over 3 inches wide, even large holes and open cavities.

Curing Time

Expanding foam cures slower, over an hour or more after dispensing. Spray foam cures very rapidly, within minutes of application.

Insulating Value

The R-value of cured expanding foam is around R-3.7 to R-4.5 per inch. Spray foam has a higher R-value of R-5.5 to R-6.5 per inch when installed properly.

Cost

Expanding foam costs less at $3-$6 per 12 oz can. Spray foam insulation costs $1-$7 or more per square foot installed.

Property	Expanding Foam	Spray Foam
Application Method	Self-applied from cans	Installed by trained professionals
Foam Expansion	30-100x	200-300x
Foam Density	0.5-1.0 lbs/ft3	1.5-2.5 lbs/ft3
Maximum Gap Width	3 inches	Over 3 inches
Curing Time	Over 1 hour	Minutes
R-Value Per Inch	R-3.7 to R-4.5	R-5.5 to R-6.5
Cost	$3-$6 per 12oz can	$1-$7 per square foot installed

Uses for Expanding Foam vs Spray Foam

Due to their different properties, expanding foam and spray foam are suited for different applications:

Typical Uses for Expanding Foam:

• Filling small gaps around windows, doors, pipes, wires, etc
• Sealing air leaks in exterior walls
• Attaching insulation batts and panels
• Crafting, insulation projects
• Temporary insulation for odd-shaped spaces

Typical Uses for Spray Foam:

• Insulating attics, ceilings and roofs
• Insulating exterior and interior walls
• Insulating foundations and crawl spaces
• Sealing rim joists and cantilevered floors
• Air sealing HVAC systems

In summary, expanding foam works well for small DIY sealing jobs, while spray foam is used for larger professional insulation projects in new construction or renovations.

Advantages of Expanding Foam

Here are some of the advantages of using expanding foam:

• Easy to Use: Expanding foam comes ready-to-use in pressurized cans that anyone can apply.
• Affordable: Expanding foam costs just a few dollars per can, making it budget-friendly.
• Adjustable: Application can be stopped and restarted as needed to control foam volume.
• Permanent Seal: When cured, it forms a permanent airtight and watertight seal.
• Lightweight: Adds little load to structures when used for gap filling applications.
• Versatile: Can be used in many small foam sealing applications.

Advantages of Spray Foam

Here are some of the advantages of using spray foam:

• Superior Insulation: Spray foam has a higher R-value per inch than other types of insulation.
• Air Sealing: It provides excellent air sealing while insulating.
• Moisture Resistance: Closed cell spray foam resists moisture intrusion.
• Gap Filling: It can fill larger gaps, spaces and cavities.
• Adhesion: Foam bonds tightly to other building materials.
• Rigidity: Cured foam adds strength and rigidity to structures.

Disadvantages of Expanding Foam

Here are some potential disadvantages to consider with expanding foam:

• Messy: Excess foam is difficult to control and clean up.
• Hard to Remove: Fully cured foam cannot be removed easily.
• Flammable: Until cured, foam is flammable and must be handled carefully.
• Gaps Reappear: Foam may shrink slightly allowing gaps to reopen over time.
• Weak Insulation: Low R-value limits insulation ability.
• Environmental Impact: Some types use ozone-depleting blowing agents.

Disadvantages of Spray Foam

Here are some potential disadvantages to consider with spray foam:

• High Cost: Spray foam is more expensive than other types of insulation.
• Professional Installation: Proper installation requires hiring a trained professional.
• Respirator Needed: Installers must wear PPE to apply foam safely.
• Messy: Overspray must be controlled and cleaned up.
• Flammable: Wet foam is flammable until it fully cures.
• Moisture Sensitivity: Improper application can trap moisture.

Conclusion

In conclusion, expanding foam and spray foam are both polyurethane products with useful insulation and air sealing abilities. Expanding foam is convenient, affordable and easy to apply for small DIY gap filling jobs. Spray foam requires professional installation but offers superior insulation and gap filling performance ideal for large insulation projects. When selecting between the two, consider the scale of the job, the performance required, project budget and the application constraints.