Saving Energy With Loose Fill Attic Insulation

Despite the enormous advances in energy efficient materials, insulation continues to provide the most substantial return on dollars invested. Since the 1970’s, the cost of adding additional attic insulation has proven to be the single most cost effective structural upgrade when compared to competing technologies.

The Materials

Fiberglass may be the most recognized blown-in system. In the manufacturing process, molten glass is drawn through tubes from a spinning cylinder to create extremely thin strands. The fibers are interwoven to produce a pliable material that is comprised of millions of energy-trapping air pockets.

Cellulose is a loose fill material that is manufactured from paper products, including recycled newspaper. It is fibrous in nature and therefore exhibits excellent properties as a thermal barrier. The material is treated with fire retardant chemicals such as borax and boric acid which ensures its safe application when sprayed into an attic.


Heat is transferred through three methods, including conduction, convection and radiation. Cellulose and fiberglass are most effective against conductive heat transfer and therefore are evaluated by a derivative measurement called “R-value.”

Cellulose has an R-value per inch of 3.6-3.8, while fiberglass rates at 2.2-2.6. It is important to recognize that the R-value of an installation is far more relevant than the number of inches applied. Since cellulose has a higher density than fiberglass it may require less inches, but the overall job could actually cost more.


Over time, properly installed fiberglass will settle about 1%, which only marginally affects its thermal efficiency. Cellulose tends to settle as much as 20%, which substantially diminishes its R-value. It is important to calculate this reduction in performance and consider purchasing additional material to compensate.

Fire Resistance

By its nature, fiberglass is an inorganic material that is essentially non-combustible. As a paper product, cellulose is naturally flammable and therefore is treated with fire-retardant chemicals. Certain studies have provided evidence that these chemicals begin to dissipate within six months of application.

Ecological Value

Cellulose is comprised of 80% recycled paper and 20% chemical content. However, recycled paper is a high demand product and therefore the effect on the number of trees actually saved is questionable. Fiberglass uses up to 40% recycled glass in the manufacturing process, but uses more fossil fuels in its production.

Choosing a Material

Both cellulose and fiberglass have unique features and benefits that make them attractive for blown-in applications. Attic insulation upgrades are an effective method of reducing monthly energy costs and achieving an excellent return on investment.