Fiberglass is a composite material made by embedding fine glass fibers within a polymer resin matrix. This material is widely used across many industries, from construction to electronics, due to its distinct physical properties. Fiberglass is not a conductor of energy. Instead, this composite is categorized as a highly effective insulator, resisting the flow of both electrical current and thermal energy.
Fiberglass as an Electrical Insulator
The primary component of fiberglass, glass, is an amorphous solid composed mainly of silicon dioxide. This structure is inherently non-metallic and lacks the free-moving electrons necessary for electricity to flow easily. The absence of charge carriers results in extremely high resistance to electrical current. The composite structure, reinforced with non-conductive polymer resins like epoxy or polyester, further solidifies this insulating property.
The effectiveness of fiberglass as an electrical barrier is measured by its dielectric strength, the maximum electric field it can withstand before breakdown. Specialized variants, such as E-glass, are engineered for low electrical conductivity, making them suitable for applications like circuit boards and electrical housings. Fiberglass is routinely used to separate high-voltage components in equipment. It prevents unintended electrical paths, ensuring current remains confined to its intended circuit.
Fiberglass as a Thermal Insulator
Fiberglass is recognized for its function as a thermal barrier, designed to minimize the transfer of heat. Its effectiveness is primarily due to the millions of tiny air pockets trapped within the tangled fiber network, not the glass fibers themselves. These microscopic air spaces are the mechanism of insulation, as still air is a poor conductor of heat energy.
The physical structure actively works to mitigate the three forms of heat transfer. Trapped air effectively limits convection, the movement of heat through air currents, by physically immobilizing the air molecules. It also reduces conduction, the transfer of heat through direct material contact, because heat must navigate a highly circuitous path through the solid glass fibers and stagnant air. Thermal performance is quantified by the R-value, which represents the material’s ability to resist heat flow.
Conditions That Compromise Insulation
While fiberglass is an excellent insulator, its performance can be diminished by environmental factors or physical damage. Moisture is a common cause of insulation failure, affecting both electrical and thermal properties. Water readily displaces the air pockets within the fiber matrix, and because water conducts heat more easily than air, the thermal R-value drops drastically.
The presence of moisture also compromises electrical resistance, particularly if the water contains dissolved minerals or ions. These ions act as charge carriers, creating a pathway for electrical current and reducing the material’s dielectric strength. Physical damage, such as crushing or compaction of batts, severely impacts thermal performance by reducing the volume of trapped air. When the material is compressed, the density increases and the number of insulating air pockets decreases. Contamination by conductive dust, dirt, or foreign materials embedded in the surface can create unwanted electrical paths, degrading the overall integrity of the insulation barrier.