Does fiberglass insulation deteriorate over time?

Fiberglass insulation is one of the most commonly used insulation materials for homes and buildings. It is popular because it is affordable, effective, and relatively easy to install. However, some people wonder if fiberglass insulation breaks down or loses effectiveness over time. Understanding the longevity and durability of fiberglass insulation can help homeowners and builders make informed decisions about insulation needs.

Quick Answers

Here are quick answers to common questions about fiberglass insulation deterioration:

  • Fiberglass insulation does not break down or decompose over time. The glass fibers are inorganic and stable.
  • Fiberglass insulation can lose some R-value over time, but only by 1-2% per year. This decrease is gradual.
  • Proper installation is key. Insulation that is compressed or moist can lose more effectiveness.
  • UV light exposure from sunlight can damage fiberglass over time. Insulation in attics and walls is less prone to light damage.
  • Rodents or insects nesting in fiberglass can reduce its insulative properties over time by compressing it.

The Glass Wool Fibers in Fiberglass are Stable and Long-Lasting

Fiberglass insulation is made from extremely fine glass fibers bonded together with thermosetting resins. The glass wool fibers do not biodegrade or decompose over time. Glass is an inorganic material that maintains its chemical structure, even after decades of use.

Manufacturers fortify the glass with silicone coatings to prevent damage or breakdown from moisture. The thermosetting resins are rigid plastics designed for durability. So the fibers and bonding agents in fiberglass resist deterioration.

One potential downside of fiberglass is that the tiny glass fibers can irritate skin and lungs during handling. But once the insulation is enclosed behind walls, under floors, or in attics, the fibers pose no health hazard. Encapsulated fiberglass is non-toxic and chemically stable long-term.

The Glass Fibers are Thinner than Human Hair

Here are some details about fiberglass insulation materials:

  • Fiber diameters range from 0.5 to 9 microns (a human hair is about 100 microns thick)
  • insideration) to aid flowability
  • Binders (0-20% by weight) glue the fibers together and reduce dust

The extremely small glass fiber diameters provide insulating performance by trapping air. The silicones and binders give the overall insulation product stability and durability.

Gradual R-Value Loss Over Time

While the glass fibers themselves do not break down, fiberglass insulation can lose some effectiveness over decades of use. But the R-value loss is very gradual.

R-value indicates an insulation’s ability to resist heat flow. The higher the R-value, the better the insulating performance. Fiberglass batts and rolls typically have R-values between R-11 and R-21. Blown-in fiberglass ranges from R-13 to R-30.

According to insulation industry testing, fiberglass products lose only 1-2% of their original R-value per year. So if properly installed, R-19 batt insulation would decrease to about R-17 after 10 years and R-15 after 20 years.

This slow, incremental R-value loss is not usually significant enough to necessitate replacing aging fiberglass insulation.

Factors that Cause Faster R-Value Loss

While a 1-2% annual R-value loss is typical, certain circumstances can cause fiberglass insulation to deteriorate faster:

  • Moisture: Wet insulation loses effectiveness. Water can saturate batts and promote mold growth.
  • Compression: Insulation compressed to less than its intended thickness loses R-value.
  • Air infiltration: Drafts through or around insulation reduce its performance.
  • Installation issues: Gaps, compressed areas, or uneven application can decrease R-value.

Ensuring insulation stays dry, lofty, and evenly distributed helps maintain its insulation capacity long-term.

Proper Installation Increases Longevity

To get the most life out of fiberglass insulation, proper installation is key. Professional insulation contractors are trained on technique. DIYers should carefully follow manufacturer instructions.

Here are best practices for installing fiberglass batt, roll, or blown-in insulation:

  • Provide adequate ventilation to prevent condensation and moisture.
  • Install a vapor barrier on the warm side of insulation to reduce wetting.
  • Use unfaced insulation between studs and joists for the tightest fit.
  • Fit batts and rolls snugly without excess compression or gaps.
  • Evenly distribute and fluff blown-in insulation to the desired depth.
  • Don’t overfill enclosed cavities – slight underfill is better.

Achieving the correct thickness, density, and compression helps maintain optimal R-value. Leaving no gaps reduces air infiltration through the insulation. Following manufacturer specifications for installation maximizes product longevity.

Avoid Damaging Insulation During Other Construction Work

It’s also important to avoid damaging insulation already in place during other construction or renovation projects. For example, walking on attic insulation can compress it. Insulation near walls and ceilings can become compacted when drywall is installed or servicing wiring.

Care should be taken to preserve intact insulation during any work after initial installation. Protecting insulation from disturbance preserves proper thickness and insulation value.

Sunlight Can Damage Insulation Over Time

In addition to moisture and compression, ultraviolet (UV) light exposure can damage fiberglass insulation over years of use. The sun’s rays can interact with the plastic binders, reducing effectiveness.

Insulation in enclosed interior walls is completely protected from light exposure. But attic and roof insulation may be subjected to prolonged UV exposure from sunlight entering through windows, skylights, ventilation openings.

To minimize UV damage risk:

  • Cover attic insulation with protective netting or housewrap
  • Install black roofing paper below roof sheathing to block light
  • Use foil-faced insulation on attic floors and ceilings
  • Close skylights or ventilation openings not in regular use

Taking steps to shield attic and roof insulation from sunlight helps maintain long-term thermal performance.

Musty Odor May Indicate Moisture Damage

One sign of insulation deterioration is a musty, moldy smell. This odor usually means the insulation has become moisture-damaged.

Wet insulation should be dried out or replaced to maintain healthy indoor air quality and proper insulation value. Standing water also promotes mold growth in insulation over time.

It’s important to fix any roof, plumbing, or condensation problems that are introducing moisture into the insulation. Just replacing damaged insulation without addressing leaks will lead to premature failure of the new insulation.

Pests Can Reduce Insulation Effectiveness

Rodents, insects, and birds nesting in insulation can decrease its R-value over time. As creatures move through and compact the insulation, they reduce thickness and insulating performance.

Cellulose and fiberglass insulations are both vulnerable to intrusion by pests seeking shelter. Blown-in loose fill insulation in attics seems especially prone to animal infestation over time.

Signs of pest activity in insulation include:

  • Droppings
  • Nests
  • Chew holes in vapor barriers
  • Visible traffic trails through insulation

To limit pest damage, proactively seal any potential access points using:

  • Copper mesh
  • Foam sealant
  • Steel wool
  • Caulk

Trapping and removing current pests can help too. But avoiding new infiltration is key to preventing recurring issues long-term.

Replacing Damaged Insulation

If insulation becomes excessively compacted, moist, or infested, replacement may be warranted. Remove and replace any sections that have clearly lost loft and insulative capacity.

Spot replacement of damaged areas helps restore full insulating value. Complete tear out and replacement of insulation is only needed in extreme cases of widespread damage and deterioration.

Fiberglass Insulation Outperforms Other Types

Compared to other insulations, fiberglass performs very well over time. Here’s how it stacks up:


Cellulose insulation made from recycled paper settles and compacts more over time than fiberglass. Moisture also decreases cellulose’s R-value faster than fiberglass. But cellulose costs less upfront.

Mineral Wool

Mineral wool insulation shares many properties with fiberglass. But it may be slightly more vulnerable to moisture and compression damage over time.

Spray Foam

Spray foam insulation can outperform fiberglass initially. But it degrades faster over years of use due to chemical breakdown. Fiberglass holds its insulation value longer than spray foam.

EPS Foam Boards

EPS rigid foam boards lose R-value slowly when properly enclosed. But the foam can break down if exposed to sunlight. Fiberglass resists light damage better when installed correctly.

So fiberglass insulation remains a top choice for maintaining reliable thermal performance over decades. Proper installation and preventative pest control helps fiberglass retain its insulation capacity long-term.


Fiberglass insulation can serve reliably for the entire lifespan of a building. While gradual R-value loss does occur over time, fiberglass insulation does not decompose or disintegrate. The glass wool fibers remain stable and intact for decades.

To maximize the longevity of fiberglass insulation:

  • Install insulation properly at the recommended thickness and density.
  • Control moisture sources to prevent wetting and mold growth.
  • Protect attic insulation from excessive sunlight.
  • Prevent pests from nesting in the insulation through exclusions and baiting.
  • Avoid compressing or disturbing insulation after installation.

With proper care, fiberglass insulation can continue providing reliable thermal protection for 30 years or more. Its gradual R-value loss is manageable compared to more drastic deterioration seen in other types of insulation.

Fiberglass remains a very durable and long-lasting insulation. Correct installation and preventing moisture, pests, and compression helps fiberglass maintain excellent thermal performance decade after decade.

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