In composite material applications such as FRP products, marine construction, sanitary ware, and wind turbine blades, fiberglass mat is one of the most fundamental reinforcement materials. After bulk purchasing, companies rarely use the entire inventory immediately; it inevitably needs to be stored for weeks or even months. This raises a practical question that every procurement officer and technician must face: does fiberglass mat go bad over time?

What Actually Deteriorates?

In products made from glass fibers, the pure glass fibers themselves are inorganic materials with excellent corrosion resistance—they do not rot or mold. However, during use and storage, the deterioration actually occurs in the ancillary materials and composite matrices.

Here are the key components in fiberglass products that are prone to deterioration and aging:

1. Binder / Sizing

Manifestation: Fiberglass mat typically contains phenolic resins, polyesters, or other binders to hold the fiber shape during production.

Cause of deterioration: These organic binders can decompose, degrade, or hydrolyze under prolonged exposure to sunlight, moisture, or high temperatures.

Consequences: Binder failure causes the mat to become brittle, shed powder, lose structural integrity, and reduce flexibility.

2. Resin Matrix

Manifestation: When fiberglass mat is used to make composites, it must be combined with resins such as epoxy or unsaturated polyester.

Cause of deterioration: Resins are organic polymers that are highly susceptible to UV radiation, moisture, thermal cycling, and chemical attack. Moisture penetrating the resin–fiber interface accelerates delamination.

Consequences: The resin may yellow, become brittle, powder, crack, or even delaminate, leading to a significant drop in overall mechanical strength.

Forms of Deterioration in Fiberglass Mat

1. Chemical Attack and Hydrolysis

Alkaline corrosion: Medium‑ and high‑alkali glass fibers are particularly vulnerable to acids, alkalis, and other chemicals, which can corrode the surface, causing whitening or even powdering.

Hydrolysis: Under hot and humid conditions, chemical bonds such as ester linkages in the binder can undergo hydrolysis. Once hydrolyzed, the binder loses its mechanical and processing performance.

2. Photo‑Oxidation and Thermal Degradation

UV photodegradation: Prolonged exposure to sunlight or strong UV radiation—though pure glass fibers themselves have good UV resistance—can penetrate the resin and reach the interface, causing chain scission, discoloration, and embrittlement of the resin matrix, leading to debonding between fibers and resin.

Thermal stress damage: Extreme temperature fluctuations generate microscopic thermal stresses in the fibers, which can cause brittle fracture.

3. Physical Wear and Binder Loss

Dry‑mat dusting/fuzzing: Improper handling, rubbing, or vibration can loosen the fiber bundles in chopped‑strand mats, resulting in fuzz, broken filaments, or even holes.

Organic binder decomposition: When exposed to temperatures above 200°C for extended periods, the organic binder undergoes thermal degradation and carbonization, manifested as yellowing, disintegration, and odor.

Binder aging failure: If the binder expires or is compromised by environmental factors, the mat loses its original softness and conformability, becoming stiff or friable, making it difficult to lay up in complex molds.

Comparison of New vs. Deteriorated Fiberglass Mat Performance

Proper Storage Methods

Temperature and Humidity Control

1. Storage temperature: 15°C – 35°C

2. Relative humidity: 35% – 65%

3. Environmental requirements: Dry, cool, well‑ventilated; protect from rain and direct sunlight.

Packaging and Stacking

Fiberglass mats are typically packaged in polyethylene bags, then placed in cartons or wrapped in kraft paper. During storage, the following should be noted:

1. Keep original packaging: Do not open the packaging unless the mat is to be used to prevent moisture absorption.

2. Pre‑condition before use: It is recommended to place the product indoors for at least 24 hours before use to allow it to acclimate to the ambient temperature.

3. Proper stacking: Always use pallets to elevate the material off the floor. Do not stack too high, and avoid heavy compression, which can deform, damage, or compact the mat.