R-Value measures the ability of insulation to stop or slow heat transfer. In theory, the higher the R-Value, the greater the resistance will be. However, not all R-Values are created equal as it measures only one of the factors that determine how insulation will perform.
R-Values are measured in laboratory conditions and do not consider the effects of real-world circumstances on the thermal performance of insulations. There are variables that will change how insulation performs. Heat moves in and out of your home the following ways:
Cellulose insulation has excellent R-Value (prevents heat loss via conduction), is pneumatically applied filling all voids and gaps (prevents heat loss via convection and air infiltration) and is densely packed (prevents heat loss via radiation and air infiltration) meeting all four of the critical performance criteria.
Click on this map to find the insulation R-Value recommendations by U.S. regions from EnergyStar.gov.
(Sources: US Department of Energy)