The R-value measures a material's resistance to heat flow and is an indicator of a material's insulation performance. Plywood generally has an R-value of around 1.25 per inch of thickness, while drywall has an R-value of around 0.45 per ½ inch of thickness. While the R-value for plywood might seem higher, remember that drywall typically has better overall insulation properties due to its dense gypsum core, making it a more effective thermal barrier in most cases.