When properly installed, closed cell foam (spray or board) provides two benefits: first and foremost it’s a great insulator with MUCH better R values per inch than fiberglass, and secondly when you use closed cell foam that’s at least 1-1/2 inches thick, it actually acts as a vapor ...
For example: if a 1-inch thick piece of material prevents thermal transfer at a rate of 3.5 times better compared to no barrier, then 4 inches of that material would have an R-value of 14 and 6 inches would be R-21. So, a material with R 38 would be 38 times better at preventing...
If not, get to work--clear the room of furniture, and protect flooring by covering it with thick plastic sheeting taped to the baseboards. Wear a dust mask and goggles. With a heavy-napped paint roller soaked in water, wet a small area of the ceiling and scrape away the moistened ...