Whether the R-value of a garage door insulation kit is good enough for your garage is based on several factors, including the number of shared or detached walls, the heating system inside the garage (if it has one), and the average climate in your city or state. However, for most garages, an R-value of 4 to 8 is acceptable for insulating your garage door, though for maximum heat retention you can get insulation with an R-value up to 16.