Like many of you, I am wary of the global warming potential of the blowing agent used in XPS. I’ve seen that it has 1,430 times the GWP of CO2, but that isn’t really something I intuitively understand. So I did some quick and dirty math, and it looks like every square foot of 1″ thickness XPS is like driving an economy car (that gets 30mpg) for 22 miles. I was wondering about putting 1/2″ of XPS on my 800 sqft basement floor, but that would be like driving 8800 miles in a car. Now I have a real appreciation for this impact. I think I’ll stick to EPS.