The thermal properties of closed-cell foam insulation display a more complex behaviour than other construction materials due to the properties of the blowing agent captured in their cellular structure. Over time, blowing agent diffuses out from and air into the cellular structure resulting in an increase in thermal conductivity, a process that is temperature dependent. Some blowing agents also condense at temperatures within the in-service range of the insulation, resulting in non-linear temperature dependent relationships. Moreover, diffusion of moisture into the cellular structure increases thermal conductivity.

Standards exist to quantify the effect of gas diffusion on thermal conductivity, however only at standard laboratory conditions. In this paper a new test procedure is described that includes calculation methods to determine Temperature Dependent Long-Term Thermal Conductivity (LTTC_(T)) functions for closed-cell foam insulation using as a test material, a Medium-Density Spray Polyurethane Foam (MDSPF). Tests results are provided to show the validity of the method and to investigate the effects of both conditioning and mean test temperature on change in thermal conductivity. In addition, testing was conducted to produce a moisture dependent thermal conductivity function. The resulting functions were used in hygrothermal simulations to assess the effect of foam aging, in-service temperature and moisture content on the performance of a typical wall assembly incorporating MDSPF located in four Canadian climate zones. Results show that after 1 year, mean thermal conductivity increased 15%–16% and after 5 years 23%–24%, depending on climate zone. Furthermore, the use of the LTTC_(T) function to calculate the wall assembly U-value improved accuracy between 3% and 5%.

闭孔泡沫绝缘材料的热性能表现出比其他建筑材料更复杂的行为，这是由于其多孔结构中捕获的发泡剂的特性。随着时间的推移，发泡剂从多孔结构中扩散出来并进入空气，导致热导率增加，这一过程与温度有关。一些发泡剂也在绝缘材料的使用范围内的温度下冷凝，导致非线性温度相关关系。此外，水分扩散到蜂窝结构中会增加热导率。

存在量化气体扩散对热导率影响的标准，但仅限于标准实验室条件。本文介绍了一种新的测试程序，其中包括确定温度相关长期热导率 (LTTC _(T)) 用于使用中密度喷涂聚氨酯泡沫 (MDSPF) 作为测试材料的闭孔泡沫绝缘。提供的测试结果显示了该方法的有效性，并研究了调节和平均测试温度对热导率变化的影响。此外，还进行了测试以产生依赖于水分的热导率函数。所得函数用于湿热模拟，以评估泡沫老化、使用温度和水分含量对包含 MDSPF 的典型墙组件性能的影响，该墙组件位于加拿大四个气候区。结果表明，1 年后，平均热导率增加 15%–16%，5 年后增加 23%–24%，具体取决于气候带。此外，使用 LTTC _(T)计算墙组件U值的函数将精度提高了 3% 到 5%。