Additionally, closed - cell spray foam insulation lends strength to the walls and roof. (insteading.com)
The relative humidity was predicted in the center of the open - cell spray foam insulation and was found to be at safe levels (Figure 2). (buildingscience.com)
They recommend putting down a layer of spray foam first, which will air - seal the attic, then blowing in cheaper loose - fill insulation on top. (moneysense.ca)