What is the R-value of your blown-in fibreglass compared to batt insulation?

A 2 x 6 wall will perform at an R24. Batts in a 2 x 6 wall are sold to perform at an R-value of R19 to R24, but tests conducted by the National Research Council concluded that an R19 fibreglass batt with minor installation defects will only perform at an R12½. Blown-in fibreglass will always perform at the installed R-value because the insulation is manufactured onsite to a specified density that ensures a true working R-value.