Rigid Polyurethane Foam Lifespan, R Factor And Thermal Drift
Rigid polyurethane foam forms during a reaction between two polymer products with different molecular weights. Foam boards made from the material resist heat flow, and hence are useful for insulation. We consider the thermal characteristics of rigid foam as used in buildings in this short post.
Two Types of Rigid Foam with Different Thermal Characteristics
There are two categories of insulation that may be used in building construction:
- Inorganic insulation materials including glass, rock wool, slag wool, or alumina silica.
- Organic insulation materials such as wool, fiberglass, rock wool, polystyrene, and polyurethane.
We focus on organic insulation materials in this post, and specifically rigid polyurethane foam. That’s because the bulky material resists heat flow from inside or outside structures.
Please Bear With Us While We Introduce Foam Gas
An article we found in Springer International Journal of Thermo-Physics explains how the thermal characteristics of rigid foam may vary over time. The reasons for this phenomenon are as follows:
- Foam gas is used for producing organic insulation materials.
- The thermal conductivity of foam gas is typically lower than air.
- The foam gas gradually discharges, and air takes its place.
- The air has lower thermal resistance and is less effective insulation.
The article in Springer International Journal of Thermo-Physics further explains how the gas composition ratio in the air bubbles progressively changes, leading to performance degradation in rigid foam insulation materials. The first stage of this deterioration may take as long as five years, with the final phase lasting over ten years.
The Thermal Drift Characteristics of Rigid Foam Insulation Materials
We close this article by turning our attention to the practical aspects of this phenomenon in the building trade. The industry expresses the ability of a material to resist heat in terms of its ‘R Value’. This factor in turn is the insulation material’s thickness divided by its thermal conductivity.
A particular material’s R Factor is not consistent over time. Insul Foam explains how the thermal characteristics of rigid foam insulation depend on the state of the tiny cells within the polymer-based material:
- The degradation rate of a closed cell depends on the quality of its manufacture.
- The type of blowing gas used in manufacture affects the material’s long-term stability.
- This stability affects the rate of degradation, and therefore the robustness of the R Factor.
This ‘thermal drift rate’, as the insulation industry calls it, is a measure of how long foam insulation will remain effective. Choosing the right thermal insulation material – and being willing to pay for it – is a critical factor for your project’s success. Chat with Valiant Exteriors for more advice.
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