In HVAC systems, ducts not only perform air transport functions, but their internal structure also directly affects the system's energy consumption, noise control, and operational stability. Fiberglass ducts, as composite ducts integrating insulation, sound absorption, and air transport functions, have a unique internal wall structure that distinguishes them from traditional metal ducts.

This article will systematically analyze the internal wall structure of fiberglass ducts from the perspectives of structural composition, performance mechanisms, and engineering applications.

I. Basic Composition of the Inner Wall of Fiberglass Ducts

Fiberglass ducts are typically composed of a multi-layered composite structure, with the inner wall layer being the key part directly in contact with airflow. Its structure generally includes:

1. High-density fiberglass substrate layer

2. Inner surface shaping treatment layer (pressed or coated)

3. Surface reinforcement structure (depending on the model)

This structural design ensures smooth airflow while also providing sound absorption, insulation, and structural stability.

II. Main Structural Features of the Inner Wall of Fiberglass Ducts

1️⃣ Porous Structure with Uniformly Distributed Fibers

The inner wall of fiberglass ducts is composed of interlaced, slender glass fibers, forming a uniform and stable porous structure. This structure is characterized by:

Small and evenly distributed pore size

Relatively still internal air

Beneficial for reducing sound wave propagation energy

This porous fiber structure is a crucial foundation for the sound absorption performance of fiberglass ducts.

2️⃣ Dense but Not Completely Sealed Surface

Unlike loose fiber materials, the inner wall of fiberglass ducts is typically formed through compression molding, resulting in:

A relatively smooth surface

Fibers are less prone to shedding

Controllable airflow friction resistance

This "semi-dense structure" ensures the stability of airflow without completely sealing the internal sound-absorbing pores.

3️⃣ Integrated Inner Wall and Insulation Layer Design

The inner wall of the fiberglass duct is not independent but integrated with the overall duct structure:

The inner wall handles airflow contact and noise reduction.

The middle layer provides the main insulation performance.

The outer layer provides structural support and protection.

This integrated structure reduces the gaps and thermal bridging problems associated with the traditional "inner lining + outer insulation" combination in ducts.

4️⃣ Metal-Free Cold Bridge Structure on the Inner Wall

The inner wall of the fiberglass duct is made of a non-metallic material, avoiding the cold bridging phenomenon common in metal ducts. Its structural characteristics include:

Less prone to condensation

Relatively uniform temperature distribution on the inner wall

Conducive to stable system operation

This structural advantage is particularly evident in air conditioning systems with high requirements for condensation control.

III. Impact of Fiberglass Duct Inner Wall Structure on Performance

▶ Impact on Airflow Delivery

After shaping treatment, the surface roughness of the fiberglass duct inner wall is within a reasonable range. Under normal wind speed conditions:

It does not significantly increase system resistance.

Airflow distribution is relatively uniform.

It helps reduce the generation of local eddies.

▶ Impact on Noise Reduction Performance

The porous fiber inner wall structure can significantly attenuate mid-to-high frequency noise. The main mechanisms include:

Sound waves are repeatedly reflected after entering the pores.

Sound energy is converted into weak heat energy and dissipated.

It reduces the propagation of fan and airflow noise.

Therefore, fiberglass ducts possess a certain degree of noise reduction function at the inner wall structure level.

▶ Impact on System Cleanliness

The inner wall of properly manufactured fiberglass ducts undergoes curing and shaping treatment, effectively controlling:

The risk of fiber shedding.

The problem of dust flowing with the airflow.

Under normal wind speed and reasonable usage conditions, the inner wall structure possesses stability.

IV. Structural Differences Between Fiberglass Duct Inner Walls and Metal Duct Inner Walls

From a structural perspective, the two differ significantly:

Metal duct inner wall: smooth but lacks sound absorption capacity.

Fiberglass duct inner wall: porous fiber structure, combining sound absorption and thermal insulation.

Therefore, in systems requiring noise control and energy efficiency, the inner wall structure of fiberglass ducts offers certain advantages.

V. Application Value of Inner Wall Structure in Practical Engineering

In practical HVAC engineering, the structural characteristics of fiberglass duct inner walls make them suitable for:

Commercial building air conditioning systems

Office and public building supply and return air systems

Areas with high noise control requirements

Rational utilization of its structural characteristics can reduce the need for additional sound absorption measures and simplify system design.

The inner wall structure of fiberglass ducts uses porous glass fiber as its core feature, combining airflow stability, sound absorption and noise reduction, and thermal insulation. Its surface shaping and non-metallic integrated structure give the duct good overall performance during operation. In modern HVAC systems, this inner wall structure has become one of the important technological advantages of fiberglass ducts.