Comparing Polyiso and Molded Polystyrene from the past to today


We are pleased to announce Foam-Control Technical Bulletin Roofing No. 3017 is now available. The bulletin compares the performance of polyiso and Molded Polystyrene from the past to today.


A school building located in Minnesota was recently undergoing a roofing system replacement and it provided the perfect opportunity to evaluate the performance of the existing roof insulations. The school was originally built in 1999 and consisted of a combination of polyiso and molded polystyrene roof insulation. Samples of both products were removed from the roof and evaluated for R-value at various temperatures.

Testing demonstrated the vastly different temperature dependence between polyiso and molded polystyrene. A plot of the R-value for the 17 year old polyiso and new polyiso demonstrates the dramatic change in polyiso insulation in recent years. “New” polyiso loses significant R-value at cold temperatures.

In comparison, the R-value for 17 year old molded polystyrene and new molded polystyrene are similar. This demonstrates that molded polystyrene can be trusted to have stable R-value performance.

It is very important to understand that the latest generation of polyiso insulations and molded polystyrene have very similar R-values when used at cold temperatures. This has dramatic implications when selecting your insulation product and its thickness for use in cold weather and cold storage applications