Open Cell spray foam is also referred to as ½ pound or low density. This foam expands to over 120 times its liquid size, and requires trimming and disposal of the waste. Open Cell foam cures soft and the irregular bubbles which form during the expansion reaction are broken or open.
These cells or pockets fill with air, and as such the R-Value of Open Cell foam is close to that of dormant air, around 3.6 per inch. The R-Value of Open Cell foam is close to that of Conventional Fiberglass and Cellulose Insulation because they all use the same principle of trapping dormant air. However Open Cell foam is more effective than conventional insulation because it is spray applied as a liquid which conforms to fit the wall cavity. Like conventional insulation Open Cell foam only slows down convection through and within the wall cavity. Open Cell foam is not a Code Approved Vapour Barrier with a permeability rating of over 400 ng.
Closed Cell spray foam is also referred to as 2 pound or medium density. This foam expands 20 to 30 times its liquid size, and seldom requires trimming with little to no waste. Closed Cell foam cures rigid and the millions of microscopic bubbles which form during the expansion reaction remain closed and intact. This traps the reaction gases, and as such the R-Value of Closed Cell foam is close to that of the reaction gas, around 7 per inch. The Closed Cell structure is very strong; increasing shear and racking strength by 300%. Closed Cell foam is a Code Approved Vapour Barrier with a permeability rating of under 45 ng, as well as a Code Approved Air Barrier and Thermal Insulation. Closed Cell foam is spray applied as a liquid to create an air-tight seal as it expands as a foam to stop air leakage. But unlike Open Cell foam, Closed Cell foam stops both convection through and within the wall cavity. Enviro Foam is a Closed Cell spray foam.
As you increase the Cellular Structure (Density and Closed Cell Content) of Spray Foam Insulation you also increase the following Mechanical Properties, Transfer Properties, and Durability:
Compressive Strength - The physical Strength of a Urethane foam is measured by Compressive Yield Strength. Compressive Strength increases with foam density.
Tensile Strength - This parameter measures the force required to pull the foam apart, along with the degree of pre-break elongation. Higher density increases tensile strength.
Shear Strength - Shear forces operate perpendicular to accompanying strains. Shear strength increases with density.
Flexural Strength - The maximum stress in the outer fiber at the moment of crack or break. Higher density increases flexural strength.
Thermal Resistance - R-Value is the measure of a products ability to resist heat flow. R-Value for Urethane foam is optimum in the 2 - 2.4 lb. range. Below 2 lb. the difficulty in maintaining adequate closed cells and good cell structure causes decreased thermal resistance. Above 2.4 lb. conduction through the solid polymer begins to decrease the thermal resistance.
Water Vapour Permeance - The rate of water vapour penetration through a product. As density increases, water vapour permeance decreases.
Water Absorption - The amount of water picked up over a specific period of time. Water absorption decreases as density increases.
Dimensional Stability - The ability to resist physical changes under various environmental conditions. As Density increases, so does dimensional stability.
Cold Aging - To measure cold aging a sample is cooled to -29°C and the percent volume changes are measured after 1, 7, 14, and 28 days. Low density foams shrink at low temperatures. The blowing agent condenses below room temperature and the pressure reduces. Since the structure is not rigid this pressure reduction causes shrinkage.
Dry Aging - To measure dry aging a foam sample is heated to 100°C and the percent volume changes are measured after 1, 7, 14, and 28 days. Low density foams are distorted at high temperatures, as the blowing agent is lost or diluted with air.
Humid Aging - To measure humid aging a foam sample is heated to 100°C at 97% Relative Humidity and the percent volume changes are measured after 1, 7, 14, and 28 days. Low density foams are distorted at high humidity as the blowing agent is lost or diluted with moisture vapour.