R-value measures how well a material resists heat flowing through it, and higher numbers mean better resistance. Closed-cell spray foam is roughly R-6 to R-7 per inch, while open-cell spray foam is roughly R-3.5 to R-3.8 per inch. But R-value only tells part of the story, because it doesn't measure air leakage, and air leakage is where many Iowa homes lose the most heat. When you're comparing insulation quotes or reading product labels, it helps to know what the number does a