According to The Department of Energy, an "insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value." A material with a higher R-Value is more effective at insulating.  Blown-in insulation — which is relatively cheap — has lower R-values, while SIPs have higher values. Other than insulation type, the numbers also depend on the specific insulation's thickness and density. Take note that recommended R-values vary in different locations in your home (ex. walls, attic, etc).  Check out this map from Energy Star for the recommended home insulation R-Values depending on your location in the US.