When considering garage door insulation, you first need to consider the walls of your garage, the ceiling and any adjacent living spaces. Check out what building materials have been used as those will influence what affect your door choice will have on the insulation of the space.
To prevent heat loss and optimize the energy efficiency of your garage door, match the R-value of your garage door to the R-value of your garage’s walls.
R-value is the measure of resistance to heat flow through a material, but a higher R-value can not account for heat loss through the walls of your garage. Choosing a door with a higher or lower R-value than your garage currently has will have a limited effect in stopping heat transfer (but you will still want to consider an insulated door for security and durability purposes).