At the time this publication was written, the average loose-fill insulation cost per R-value per square foot was about 0.8 cents for cellulose and rock wool and 1.1 cents for fiberglass. These prices were for materials only. The average installed price per R-value per square foot was about 1.2 cents for blown-in cellulose and rock wool and 1.3 cents for fiberglass. Because prices vary in different regions, obtain bids from several insulation contractors or suppliers to determine the specific cost in your area.