Cellulose vs. Fiberglass Attic Insulation

The following is a summary of an extensive Natural Resources Defense Council (NRDC) report.

The NRDC has concluded the following:

  • Cellulose insulation manufactured from recycled paper is the least polluting and most energy efficient insulation.
  • Cellulose has the highest post-consumer recycled content.
  • The fiberglass industry averages 35% recycled glass, while the cellulose industry averages a minimum of 75% recycled content.
  • It takes more than 10 times as much energy to produce fiberglass insulation as cellulose insulation.
  • Due to air circulation and natural convection, the R-value of blown-in fiberglass insulation decreases by as much as 50% as the temperature drops from 45 degrees F to 18 degrees
  • Substantial and well-documented public health threats are associated with fiberglass. There no adverse health effects from cellulose insulation have been identified.
  • Bottom line when the temperature in the attic is 20 degrees, the fiberglass insulation in the attic will lose 40 percent of its R value. The researchers at ORNL recommended that  attics with fiberglass insulation are covered with as little as 3 inches of cellulose to stop the loss of R-value in the fiberglass. Cellulose is non-toxic. Biologically, cellulose is innocuous.
  • Researchers at Oak Ridge National Laboratory (ORNL) tested insulation under “real world” conditions in a full-scale attic simulator. Their research found that fiberglass products declined as much as 40% in R-value as the temperature difference between conditioned (inside) air and ambient (outside) air increased.

– Dr. Arthur Furst, Toxicologist

Natural Resources Defense Council


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