But insulation continues to be selected for its perceived field performance, rather than on the basis of accurate laboratory tests and, in many cases, scientists have yet to develop lab tests to simulate the field. Older insulations were extensively tested under both field and laboratory conditions, but this has not been done with many of the newer products. When observed in the field, it became apparent that convective cells caused a significant reduction in thermal performance, but since laboratory testing did not simulate these interactions between heat and air flows, it did not predict this decline in field performance. In response to these findings, a Canadian insulation manufacturer developed a new product which was immune to convective effects, and the Canadian Standards Association modified its standard to require that loose-fill products achieve a minimum thermal resistance. Manufacturers in the United States did not follow suit.
Air movements can compromise the thermal performance of glass-fibre in wall applications as well.
They are made into boards in the factory or sprayed in place in the field. Originally there is no air in the cells, only the blowing agent, but eventually the outside air diffuses into the foam and the blowing agent diffuses outward, changing the mixture of gases in the cells. The challenges for scientists studying foam insulations have been to develop laboratory techniques and perform rapid tests that accurately predict what would happen in the field many months or years later. Scientists at the Institute for Research in Construction have developed a methodology for assessing performance and life-span using ultrathin layers of insulation material ranging in thickness from 5 to 10 mm. This technique allows researchers to simulate up to 25 years of thermal performance in 6 months, and is being validated by comparing predicted results with those measured on samples exposed to controlled laboratory and field conditions.