In building and construction, R-value is a measure of how well an object, per unit of its exposed area, resists conductive flow of heat: the greater the R-value, the greater the resistance, and so the better the thermal insulating properties of the object. The wall insulation pictured bellow has an R value of 3.8 per inch, and the exterior has a continuous 2" of insulated Zip sheathing, adding an insulating R value of 9.6. The total wall section has an R-value of 32, far greater than the code required R-19.
Curious about insulating with damp spray cellulose? Read more here, and scroll down to see some before and after drywall photos.