Fiberglass Insulation Pros and Cons

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R-values of loose-fill insulationThere are three main types of conventional loose-fill insulation used in the walls and ceiling of residential and commercial buildings: fiberglass, cellulose and mineral wool . Each has certain advantages and disadvantages. This article looks at the first of the three – fiberglass insulation.

What is it?

Fiberglass insulation is the most popular insulation available today. It is sold in two forms: blankets (either long rolls or batts) and loose fill. The former comes with paper backing, for installation between the studs in walls and the joists in floors, or with no backing, for use in ceilings. The latter is mostly used in ceilings, though it can also be blown into wall cavities.


  • Fiberglass insulation is inexpensive and effective.
  • Fiberglass does not shrink.
  • Most manufacturers supply the material in sealed batts, covered with plastic film (perforated polyethylene or polypropylene, specifically) to avoid issues with breathing the fibers.
  • The plastic covering on fiberglass batts acts as an effective vapor barrier.
  • Fiberglass insulation does not burn.
  • Some fiberglass insulation uses recycled glass, reducing its ecological footprint.
  • Fiberglass insulation is available in medium- and high-density options (roughly R-11 and R-15 for a standard 2-by-4 wall).
  • Insects do not eat fiberglass insulation (or rather, it is not nutritive to them, so they have no reason to nibble).
  • Blown fiberglass surrounds everything inside wall cavities, providing a more consistent layer of insulation.



  • Protective gear must be worn when installing fiberglass insulation: the tiny slivers will lodge in skin and are small enough to be inhaled.
  • Unless you use plastic-sealed batts, fiberglass insulation requires a vapor barrier to protect it from moisture.
  • Fiberglass blankets do not seal wall and ceiling spaces very tightly.
  • Inhaled slivers of fiberglass irritate the alveoli and can cause lung disease.
  • There is some data which suggests fiberglass in the lungs may cause cancer, by slicing DNA and causing cell mutation, in the same way as mineral wool.
  • Some fiberglass insulation still uses formaldehyde as a binder, which leaks out into the air. This product may also cause cancer.
  • Fiberglass settles and sags, so its R-value decreases over time.
  • Standard fiberglass can be crammed into smaller spaces to improve its R-value, but it needs venting if this is done (to avoid moisture buildup which will destroy its efficiency).