Thermal Resistance and Aging of Rigid Urethane Foam Insulation Available to Purchase

Relevant data and analyses for aging and effective thermal conductance of rigid urethane and isocyanurate foam are reviewed. Simplified theoretical models are formulated that indicate the order of magnitude and limiting bounds for exact results. Existing heat transfer models underpredict the measured thermal conductance by 25 percent. The discrepancy is most probably caused by thermal radiation transmission through cell walls. Effective diffusion coefficients reported in the literature for different foam samples vary by an order of magnitude. The differences are caused by variations in cell geometry and cell wall permeability.