Learning the Difference Between 1/2-lb and 2-lb Spray Foam
Spray foam has become popular for its insulation value and air barrier qualities. The plastic material comes in two basic types—[0.2-kg] 1/2-lb and [0.9-kg] 2-lb—and both are used in insulation applications as barriers in buildings. Both of these foams also can help control condensation within buildings and have other environmental benefits.
2-lb SPF can be applied in multiple lifts to achieve various thicknesses for desired R-value and air barrier performance.
1/2-lb foam weighing between 6.4 kg/m3 and 9.6 kg/m3 (0.4 pcf and 0.6 pcf) when fully cured. Spray-applied to a substrate, it expands about 150 times its original volume to form a semi-rigid, non-structural plastic. This foam typically has an R-value of approximately 3.5 per 25.4 mm (1 in.) and typically uses water as the blowing agent. R-value measures resistance to heat flow—the higher the R-value, the greater the insulating power.
2-lb foam, on the other hand, weighs between 24 kg/m3 and 32 kg/m3 (1.5 pcf and 2 pcf) when fully cured. The material is used in interior applications, spray-applied to a substrate, before expanding about 35 to 50 times its original volume, and forming a rigid plastic with a compressive strength between 103.4 kPa and 172.4 kPa (15 psi and 25 psi). This foam has an (aged) R-value of around 6 per 25.4 mm (1 in.)
Spray foam similarities
As mentioned above, both the 1/2-lb and 2-lb SPFs share many common characteristics. These common qualities are detailed below.
Sealing characteristics
The air barrier system within the building envelope is an important element for controlling moisture/heat transfer, and for preserving structural integrity. Inadequate air barrier systems allow leakage of air through holes, cracks, and gaps in the building envelope. Field experience shows properly installed foam can help significantly improve the energy efficiency of buildings when used as an air leakage control and insulation system. Since 1/2-lb and 2-lb foam is applied as a liquid, it expands in all directions, filling and effectively sealing hundreds of cracks in walls, ceilings, corners, joints, and penetrations that would otherwise allow air ingress.
Thermal barriers
All foam plastic insulation is required by building codes to have a 15-minute thermal barrier covering the insulation on interior applications, unless the application exempted in the code has been approved by a building code official. Approval in this case would be based on full-scale fire tests specific to the particular situation.
Both types of foams can work well in most attics and cathedral ceilings without the
need to ventilate. However, ventilation ducts can maintain desired temperatures more efficiently
because they are in a conditioned space.
Determining the differences between Foams
Despite the shared qualities between 1/2-lb and 2-lb spray foams, it is each foams type’s unique properties that ultimately assist in selecting the proper material for the project.
1/2-lb foam is normally spray-applied to the desired thickness with one pass, while 2-lb foam is spray applied at lifts from 12.7-mm to 38-mm (0.5-in. to 1.5-in.) until the desired total thickness is achieved. Excess foam can be trimmed easily with saws or knives, however, most applications do not require full stud thickness, meaning trimming is usually, unnecessary. For example,foam installed at 51-mm (2-in.) thickness between 2x4 studs requires a minimal cleaning on the stud face. However, foam installed to full stud thickness requires additional trimming with a specially designed trimming tool.
Sound absorption
Both 1/2-lb and 2-lb foams have air barrier qualities that can help reduce noise from outside the building envelope (i.e. airplanes and car traffic). The 1/2-lb foam’s density offers additional sound absorbing qualities, however, neither foam is exceptionally effective at reducing vibrational impact noises.
Permeance
Moisture has two primary means for entry into/through the building envelope—water vapor diffusion and air leakage. As mentioned above, the excellent air barrier qualities of both 1/2-lb and 2-lb foam helps effectively preclude the latter, however, the foam types differ when it comes to vapor diffusion.
The higher the material’s permeance, the faster water vapor can pass through. Controlling water vapor within a building is important for preventing condensation, mold growth, and subsequent damage to building components. There are two basic types of moisture control within buildings:
1. The ‘flow-through design,’ which allows water vapor to pass through the building assembly’s components without condensing.
2. The vapor retarder design, which limits the moisture entering the building assembly altogether.
A 1/2-lb foam ranges between 6 perms and 10 perms, with a 76-mm (3-in.) thickness of material. Its high permeability allows for the fairly rapid diffusion of water vapor, so the material often requires a vapor retarder element in the building assembly. In some cases, this could be part of the assembly, and requires no additional vapor retarder material. (When this is necessary, it is typically used on the insulation’s warm side.)
2-lb foam typically has a permeance of less than 1 perm at 76-mm (3-in.), and can be used in flow-through designs without a vapor retarder. Exceptions include situations where there is a constant vapor drive in one direction (i.e. natatoriums and cold storage facilities), or when there is a vapor retarding material on the assembly’s cool side.
Water absorption
1/2-lb foam has a high open-cell content (greater than 50 percent) and liquid water can enter the foam. Conversely, 2-lb foam has a high closed-cell content (greater than 90 percent) and resists water absorption. In a building assembly, the latter foam offers added weather or rain barrier protection.
2-lb SPF can be applied in multiple lifts to achieve various thicknesses for desired R-value and air barrier performance.
1/2-lb foam weighing between 6.4 kg/m3 and 9.6 kg/m3 (0.4 pcf and 0.6 pcf) when fully cured. Spray-applied to a substrate, it expands about 150 times its original volume to form a semi-rigid, non-structural plastic. This foam typically has an R-value of approximately 3.5 per 25.4 mm (1 in.) and typically uses water as the blowing agent. R-value measures resistance to heat flow—the higher the R-value, the greater the insulating power.
2-lb foam, on the other hand, weighs between 24 kg/m3 and 32 kg/m3 (1.5 pcf and 2 pcf) when fully cured. The material is used in interior applications, spray-applied to a substrate, before expanding about 35 to 50 times its original volume, and forming a rigid plastic with a compressive strength between 103.4 kPa and 172.4 kPa (15 psi and 25 psi). This foam has an (aged) R-value of around 6 per 25.4 mm (1 in.)
Spray foam similarities
As mentioned above, both the 1/2-lb and 2-lb SPFs share many common characteristics. These common qualities are detailed below.
Sealing characteristics
The air barrier system within the building envelope is an important element for controlling moisture/heat transfer, and for preserving structural integrity. Inadequate air barrier systems allow leakage of air through holes, cracks, and gaps in the building envelope. Field experience shows properly installed foam can help significantly improve the energy efficiency of buildings when used as an air leakage control and insulation system. Since 1/2-lb and 2-lb foam is applied as a liquid, it expands in all directions, filling and effectively sealing hundreds of cracks in walls, ceilings, corners, joints, and penetrations that would otherwise allow air ingress.
Thermal barriers
All foam plastic insulation is required by building codes to have a 15-minute thermal barrier covering the insulation on interior applications, unless the application exempted in the code has been approved by a building code official. Approval in this case would be based on full-scale fire tests specific to the particular situation.
Both types of foams can work well in most attics and cathedral ceilings without the
need to ventilate. However, ventilation ducts can maintain desired temperatures more efficiently
because they are in a conditioned space.
Determining the differences between Foams
Despite the shared qualities between 1/2-lb and 2-lb spray foams, it is each foams type’s unique properties that ultimately assist in selecting the proper material for the project.
1/2-lb foam is normally spray-applied to the desired thickness with one pass, while 2-lb foam is spray applied at lifts from 12.7-mm to 38-mm (0.5-in. to 1.5-in.) until the desired total thickness is achieved. Excess foam can be trimmed easily with saws or knives, however, most applications do not require full stud thickness, meaning trimming is usually, unnecessary. For example,foam installed at 51-mm (2-in.) thickness between 2x4 studs requires a minimal cleaning on the stud face. However, foam installed to full stud thickness requires additional trimming with a specially designed trimming tool.
Sound absorption
Both 1/2-lb and 2-lb foams have air barrier qualities that can help reduce noise from outside the building envelope (i.e. airplanes and car traffic). The 1/2-lb foam’s density offers additional sound absorbing qualities, however, neither foam is exceptionally effective at reducing vibrational impact noises.
Permeance
Moisture has two primary means for entry into/through the building envelope—water vapor diffusion and air leakage. As mentioned above, the excellent air barrier qualities of both 1/2-lb and 2-lb foam helps effectively preclude the latter, however, the foam types differ when it comes to vapor diffusion.
The higher the material’s permeance, the faster water vapor can pass through. Controlling water vapor within a building is important for preventing condensation, mold growth, and subsequent damage to building components. There are two basic types of moisture control within buildings:
1. The ‘flow-through design,’ which allows water vapor to pass through the building assembly’s components without condensing.
2. The vapor retarder design, which limits the moisture entering the building assembly altogether.
A 1/2-lb foam ranges between 6 perms and 10 perms, with a 76-mm (3-in.) thickness of material. Its high permeability allows for the fairly rapid diffusion of water vapor, so the material often requires a vapor retarder element in the building assembly. In some cases, this could be part of the assembly, and requires no additional vapor retarder material. (When this is necessary, it is typically used on the insulation’s warm side.)
2-lb foam typically has a permeance of less than 1 perm at 76-mm (3-in.), and can be used in flow-through designs without a vapor retarder. Exceptions include situations where there is a constant vapor drive in one direction (i.e. natatoriums and cold storage facilities), or when there is a vapor retarding material on the assembly’s cool side.
Water absorption
1/2-lb foam has a high open-cell content (greater than 50 percent) and liquid water can enter the foam. Conversely, 2-lb foam has a high closed-cell content (greater than 90 percent) and resists water absorption. In a building assembly, the latter foam offers added weather or rain barrier protection.
2lb Closed Cell Spray has the highest R-value as compared to all other available types insulation products
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