Many people use “fiberglass” and “glass fiber” interchangeably – but in fact, they are not the same.
Glass fiber is the raw reinforcement – fine filaments drawn from molten glass.
When these fibers are combined with a polymer resin, they form fiberglass composites, technically known as GFRP (Glass Fiber Reinforced Polymer) – the strong, lightweight, and corrosion-free material behind Pulwell’s innovative composite products.
This article explains how glass fiber is made, its main types and properties, and how Pulwell transforms it into advanced GFRP composites used in construction, infrastructure, marine, transportation, electrical, industrial, agriculture, and more.
1. What Is Glass Fiber?
Glass fiber (or glass fibre) consists of numerous extremely fine strands of glass, typically 13–24 microns in diameter.
It is one of the most important reinforcing materials in the composites industry, offering a balance of strength, affordability, and corrosion resistance.
Common Types of Glass Fiber
- E-glass: Alumino-borosilicate glass with <1% alkali oxide; most commonly used in GFRP.
- ECR-glass: High chemical and electrical resistance; used in harsh or acidic environments.
- D-glass: Borosilicate glass with a low dielectric constant, ideal for electronic applications.
- R-glass: Aluminosilicate glass without MgO/CaO, designed for high mechanical performance.
- S-glass: Aluminosilicate with high MgO content, offering superior tensile strength.
At Pulwell, we primarily use direct rovings and continuous strand mats as core reinforcements for pultruded and roll-wrapped GFRP profiles.
2. How Glass Fiber Roving Is Made
The direct roving process is central to modern composite manufacturing and involves several precision steps:
Step 1: Melting the Raw Materials
Silica sand, limestone, and alumina are melted at over 1,400°C in a furnace, creating molten glass – the foundation for strong and consistent fibers.
Step 2: Fiberizing the Glass
Molten glass flows through a bushing plate with hundreds of micro-holes, forming continuous filaments. These filaments are rapidly drawn to maintain uniform diameter and strength.
Step 3: Applying the Sizing
A sizing solution is applied immediately after fiber formation to:
- Protect fibers from mechanical damage
- Enhance resin compatibility (epoxy, polyester, vinyl ester, etc.)
- Improve processing and wet-out performance
- Each sizing formulation is customized based on the intended application and resin system.
Step 4: Forming Direct Roving
The filaments are gathered into a single untwisted bundle and wound directly onto a package.
This “direct” method ensures:
- Uniformity and low fuzz
- Excellent resin wetting
- High compatibility with automated pultrusion and filament winding
Step 5: Packaging
Rovings are wound into rolls of 15–20 kg each and carefully packaged to prevent deformation and moisture absorption.
3. Properties of Glass Fiber Roving
| Property Type | Description |
|---|---|
| Density | 2.5–2.6 g/cm³ |
| Tensile Strength | 2,000–3,200 MPa |
| Elastic Modulus | 70–90 GPa |
| Melting Point | 1,200–1,400°C |
| Thermal Conductivity | 0.035–0.045 W/m·K |
| Water Absorption | <0.1% |
| Electrical Insulation | Excellent (non-conductive) |
| Fire Resistance | Non-combustible |
Chemically, glass fiber is resistant to alkali, bleach, and organic solvents, but can be affected by strong acids at high temperatures.
It does not rot or attract pests, making it highly durable in marine and outdoor environments.
4. Why Glass Fiber Matters for Pulwell’s GFRP Products
Fiberglass composites (GFRP) combine glass fiber reinforcement and a polymer matrix to create materials with high strength-to-weight ratio and exceptional corrosion resistance.
The fibers provide mechanical performance, while the resin distributes stress and protects the structure.
Depending on the end use, Pulwell selects and optimizes fiber type, surface treatment, and orientation.
Our Fiber Selection Strategy
- Standard E-glass: For general products such as fiberglass fence posts and agricultural stakes.
- ECR or S-glass: For demanding applications like GFRP rebars, GFRP dowel bars, and structural reinforcements.
At Pulwell, every reinforcement material – from roving to mat – is selected based on its resin compatibility and mechanical performance to meet customers’ exact specifications.
5. From Glass Fiber to Fiberglass Composites (GFRP)
GFRP materials give engineers and architects unmatched design freedom.
By adjusting fiber direction, resin matrix, and process type (pultrusion, roll-wrapping, filament winding), Pulwell delivers customized composite parts that meet diverse structural and environmental needs.
We assist customers throughout the process – from concept and design to tooling and final production – ensuring that every product achieves the desired balance of strength, durability, and cost-effectiveness.
Explore Pulwell’s composite technology and manufacturing capabilities to learn how we turn science into performance.
6. Conclusion
From the precision drawing of glass filaments to the engineering of GFRP composites, Pulwell transforms raw materials into advanced solutions that strengthen the world’s infrastructure, energy systems, and agricultural productivity.
As a leader in FRP innovation, Pulwell continues to expand the boundaries of what fiberglass composites can achieve – lighter, stronger, and more sustainable materials for every industry.