Selection guide glass fibre fabric

The Finish and its suitability for epoxy resins

FK144: Majority for aerospace, hand laminates
FE600: Electro-epoxy resin
FE800: Electro-epoxy resin/ aerospace prepreg epoxy

Glass fibres

Production of glass fibres

Glass fibers made of E-Glass are the most widely used reinforcing material. The strength properties correspond to those of metals (e.g. aluminum alloys), while the specific weight of laminates is lower than that of metals. E-Glass fibres are incombustible, heat resistant up to approx. 400 °C and resistant to most chemicals and weathering.

Production

Glass fibres are produced by the melt spinning process (jet drawing, rod drawing and jet blowing processes). The nozzle drawing process: using gravity, the hot glass mass flows through hundreds of nozzle holes of a platinum spinning plate. The elementary filaments can be drawn in unlimited length at a speed of 3 - 4 km/minute.

The glass, which is brittle in itself, has high flexibility and break resistance when drawn out into a thin thread. The elementary filaments have a titer (diameter) of approx. 9 - 15 µm and, bundled into 100 or more and provided with a protective twist, result in the filament yarn, which is further processed into glass filament fabrics (formerly glass silk fabrics).

E-Glass

E-Glass fibres have gained the greatest importance for plastic reinforcement. E stands for electro-glass, as it was originally used primarily in the electrical industry.
For the production of E-Glass, glass melts are made from pure quartz with additives of limestone, kaolin and boric acid. In addition to SiO2 (silicon dioxide), they contain different amounts of various metal oxides. The composition determines the properties of the products.

Technical data of E-Glass:

Thermal properties

Textile glass is incombustible. However, if fabrics are finished with organic agents, the fire behavior is changed. Flammability must then be assessed on the end product. Textile glass fabrics have a high residual strength after exposure to temperature.

Residual tensile strength of fabrics made of E-glass after 24 hours of storage:

Chemical properties

Glass is resistant to oils, greases and solvents and shows good resistance to acids and alkalis up to pH values of 3 - 9. Acids dissolve certain atoms from the glass surface, which leads to embrittlement. Alkalis slowly wear away the glass surface.

Acetic acid up to 15
Nitric acid < 30 %
Hydrochloric acid 15 - 30 %
Sulfuric acid < 30 %
ammonia 15 - 30 %
Caustic soda < 30 %
hydrogen chloride (after 30 minutes) 25 %

Glass filament fabric

In weaving, the types of weave commonly used in textile technology are possible, mostly plain weave, twill and atlas. The properties are determined by the weave type, yarn count and setting (thread count/cm).

All fabrics for plastic reinforcement are impregnated with special adhesion promoters:

Silane fabrics have good strength; they are suitable for polyester and epoxy resins.
Finished fabrics are equipped with modified silane sizing agents. They have a slightly tacky feel, impregnate quickly with resin, are very pliable and hardly fray when cut.

R&G carries finished brand-name fabrics from Interglas-Technologies.
Most products are qualified for aircraft construction according to material performance sheets (WLB). Epoxy resin is the primary matrix used. However, good strength values can also be achieved with polyester, vinyl ester and phenolic resins.

Finishes with aviation certification
FE800 is based on amino silane and has a firmer handle and is more stable and rigid in processing.
FK144 is based on chrome 3 and has a soft handle and very high drapability.

Both finishes can be used for the common resins and have very good strengths in the laminate, also both have aviation approval. It rather depends on the further processing of the fabric which of the mentioned properties is preferred.

Why finished glass fabrics?

Glass filament yarns are given a textile sizing by the fiber manufacturer to protect the yarn during the processing stages (warping, weaving). This sizing consists of starch and oils and counteracts adhesion between fiber and resin.
To achieve good adhesion, the textile sizing is removed from CS-Interglas fabrics and the fabric is subsequently coated with an adhesion promoter (finish). The adhesion promoters are usually modified silanes that have been adapted to the matrix material. The processing properties of the fabrics, such as drapability and impregnation behavior, are again significantly improved in a second finishing process.
Silane sizing represents a compromise between textile sizing and finishing. Here, the yarn is coated with a sizing containing adhesion-promoting silane and lubricants as processing aids. Although the properties in the textile processes are inferior to those of the textile sizing, there is no need for aftertreatment after weaving.

Processing

Finished fabrics are softer and more pliable. When laminating, the impregnation is better and the impregnation speed is significantly higher. Crystal clear laminates can therefore only be achieved with finished fabrics.

Strength properties

The adhesion of finished fabrics to the resin is better than that of fabrics with silane sizing and significantly better than that of fabrics with textile sizing, especially after exposure to moisture. Cloudiness of laminates of textile-sized and silane-sized fabrics under exposure to moisture illustrates the impaired adhesion. A measure of the quality of adhesion is the interlaminar shear strength (ILS). However, not only the shear strength but also the tensile strength is influenced by adhesion, since the distribution of an applied tensile force among the individual fibers causes shear forces. The tensile strength of silane fabrics is slightly better (without moisture) than that of finished fabrics.

Summary

Laminates of finished fabrics are clearly superior in tensile strength and interlaminar shear strength to laminates of fabrics with textile sizing. In particular, the superiority is evident in the interlaminar shear strength, which not only evaluates the adhesion of the individual fabric plies to each other but is also a parameter for durability under load.
The slightly better tensile strength of laminates made from silane-sized fabrics is usually of no significance in practice, since pure tensile stress occurs only rarely and failure very often results from delamination and the effects of moisture.

Dyed/metalized yarns

Glass fibers can be "dyed" by a special surface treatment. Black dyed glass fabric types that can be used as a cost-saving second layer for carbon fiber face laminates (carbon design). Metalized surfaces are another design variant.

Rovings - more than just reinforcement for profile drawing

Textile glass rovings consist of one or a certain number of almost parallel glass spinning threads, which are combined into one strand without twisting. Rovings are further processed into roving fabrics, chopped textile glass (glass fiber chips), mats and short fibers. In various manufacturing processes, e.g. winding and profile drawing (strand drawing), rovings are used directly as reinforcement.
Roving fabrics made from textile glass rovings are of particular importance. They can be used to produce thick moulded parts (e.g. in mold making) from a few layers. The fiber content and strength are much higher than for mat laminates but lower than for glass filament fabrics.
Fiber spray rovings immediately disintegrate into individual filaments after cutting. Rovings for winding and hand lay-up (Glass rovings) are much finer and have better cohesion.

Textile glass mats

Textile glass mats for hand lay-up are made by randomly layering cut glass spun threads (cut mat). They are bonded by a binder that dissolves in the styrene of the polyester or vinyl ester resin so that the fibers float freely in the resin. In other resins (epoxy), the mat remains completely rigid.

Cut textile glass

Glass rovings are cut into various lengths for processing in filling and molding compounds. R&G stocks the length 3 mm.
Textile glass short fibers are glass spun threads shredded to lengths of less than 1 mm and split into individual fibers. R&G stocks a ground glass fiber with a length of 0.2 mm.

Toxicity and storage

Glass fabrics do not contain any substances that are hazardous to health or toxic. Due to the filament diameters (greater than 4 µm) and the chemical structure of the glass, no carcinogenic effects occur according to current knowledge. The maximum permissible workplace concentration of glass dust is 6 mg/m³ (fine dust). No hazards occur during the transport and storage of glass fabrics. According to the Ordinance on Hazardous Substances, glass fabrics do not have to be labeled. There is no risk to persons or the environment during storage and shipping. Even at high temperatures, glass does not decompose into toxic components and is therefore harmless even in the event of a fire.

When storing glass fiber reinforcements, it must be borne in mind that the coating is sensitive to moisture. Dry, not too cool rooms are best for storage.

If the reinforcing material is stored in rooms that are too cold, the water vapor contained in the warm air will precipitate when it is brought into warm workrooms. In this case, as a precaution, the fiberglass material should be stored in the workshop for at least 8 hours before processing.

Fibreglass combines relatively high tensile strength with low weight, electrical insulation properties and good resistance to moisture and many chemicals. It is also considerably less expensive than carbon fibre, making it the material of choice for large-volume applications where cost efficiency matters.

Production of Glass Fibres

The production of glass fibres begins with the melting of raw materials - primarily silica sand, limestone, kaolin clay, and various oxides - at temperatures of around 1,400–1,600 °C. The molten glass is then extruded through a bushing plate containing hundreds of fine holes, drawing the glass into continuous filaments as it cools.

The filaments are immediately coated with a chemical sizing - a surface treatment that serves several purposes: it protects the fibres from abrasion during handling, improves the adhesion between the glass fibre and the resin matrix, and can be tailored to optimise compatibility with specific resin systems (e.g. epoxy or polyester).

The coated filaments are then gathered into strands and wound onto bobbins as rovings, or woven, knitted, or stitched into the various fabric architectures used in composite processing.

The Different Types of Fibreglass

Not all glass fibres are the same. Several compositional variants have been developed, each optimised for specific performance requirements:

• E-Glass (Electrical Glass): By far the most widely used type, E-glass offers a well-balanced combination of tensile strength, stiffness, electrical insulation, and moisture resistance at a competitive price point. It is the standard choice for the vast majority of composite applications, from boat building to construction reinforcement.
• S-Glass (Structural Glass): S-glass contains a higher proportion of silica and magnesium oxide, giving it significantly higher tensile strength and stiffness than E-glass - roughly 40% stronger. It is used in demanding structural applications such as aerospace components, ballistic armour, and high-performance sporting goods, where its higher cost is justified by the performance gains.
• ECR-Glass (Corrosion-Resistant Glass): A variant of E-glass with improved resistance to acids and alkalis, ECR-glass is used in applications where chemical attack is a concern - such as pipes, tanks, and chemical processing equipment.
• D-Glass (Dielectric Glass): Optimised for low dielectric constant and loss, D-glass is used in applications requiring minimal electromagnetic interference, such as radomes and printed circuit boards.
• AR-Glass (Alkali-Resistant Glass): Developed specifically for use in cement and concrete reinforcement, AR-glass contains zirconium oxide to resist the highly alkaline environment of cementitious matrices.

For most composite laminating work - and for the products available at R&G - E-glass and S-glass are the most relevant types.

The Characteristics of Fibreglass

Understanding the key properties of glass fibre helps in selecting the right material and designing effective laminates:

• Tensile strength: E-glass fibres have a tensile strength of approximately 3,400–3,500 MPa; S-glass reaches up to around 4,600 MPa. These values relate to the pure fibre - in a composite laminate, effective strength depends on fibre volume fraction, fibre orientation, and resin quality.
• Density: At approximately 2.54 g/cm? (E-glass), glass fibre is heavier than carbon fibre (approx. 1.78 g/cm?) or aramid (approx. 1.44 g/cm?), but still far lighter than metals such as aluminium or steel.
• Stiffness (modulus): E-glass has a tensile modulus of approximately 70–73 GPa - comparable to aluminium, but lower than carbon fibre (230–700 GPa depending on grade). For stiffness-critical applications, carbon fibre or hybrid laminates may be preferable.
• Electrical insulation: Glass fibre is an excellent electrical insulator, which makes it valuable in electrical and electronic applications.
• Chemical and moisture resistance: Glass fibre composites show good resistance to many chemicals, oils, and solvents. Moisture absorption is low, though prolonged exposure to water can gradually reduce mechanical performance - particularly in polyester-based laminates.
• Thermal properties: Glass fibre retains its structural integrity up to relatively high temperatures compared to polymer matrices; the practical temperature limit of the composite is typically governed by the resin system used.
• Optical transparency: Glass fibres are inherently transparent to light, a property exploited in optical fibres and certain decorative applications.

Which Industries Rely on Fibreglass?

The versatility and cost-effectiveness of fibreglass have made it a foundational material across a broad range of industries:

• Marine and boat building: Fibreglass has dominated boat hull construction for decades, offering excellent resistance to water, ease of moulding into complex shapes, and long service life.
• Wind energy: The blades of wind turbines are almost exclusively manufactured from glass fibre composites, where the combination of stiffness, fatigue resistance, and cost efficiency is essential at the scale required.
• Automotive and transportation: Glass fibre composites are used extensively in body panels, bumpers, underbody components, and structural reinforcements — particularly in commercial vehicles, buses, and rail applications.
• Aerospace: Whilst carbon fibre dominates primary aerospace structures, glass fibre is used in secondary structures, radomes, fairings, and interior components where its lower cost and adequate strength are sufficient.
• Construction and civil engineering: Glass fibre reinforced polymers (GFRP) are increasingly used as rebar substitutes in concrete structures, offering corrosion immunity that steel cannot provide in aggressive environments.
• Sporting goods and leisure: Surfboards, kayaks, helmets, bicycle components, and a wide range of other sporting equipment rely on glass fibre for its toughness, formability, and value.
• Electronics: Printed circuit boards (PCBs) are almost universally built on FR4 - a woven E-glass/epoxy laminate - making fibreglass a literally ubiquitous presence in modern electronics.

FAQ – Glass Fibre and Fibreglass

Is fibreglass harmful to humans?

Glass fibres can cause irritation to the skin, eyes, and respiratory tract upon contact or inhalation, particularly during cutting, sanding, or machining. Short-term skin contact typically causes itching and mild irritation. Inhalation of fine glass dust over prolonged periods without adequate respiratory protection may pose a risk to lung health. With proper personal protective equipment - gloves, safety glasses, and an appropriate dust mask or respirator - the risks associated with working with glass fibre can be effectively managed. Always observe the safety data sheets for the specific products you are using.

Why was fibreglass banned?

Fibreglass as a composite reinforcement material has not been broadly banned. The question likely stems from concerns raised in the past about certain refractory ceramic fibres (RCF) - a different class of high-temperature fibre - which are classified as potentially carcinogenic and are subject to strict occupational exposure limits in many countries. Standard glass fibres used in composite construction (E-glass, S-glass) are not classified in the same category, though sensible precautions during processing are always advisable.

What are other names for fibreglass?

Fibreglass goes by several names depending on context and region: glass fibre, glass-reinforced plastic (GRP), glass-reinforced polymer, fibreglass reinforced plastic (FRP), and - in American English - simply fiberglass. In structural engineering contexts, the abbreviation GFRP (glass fibre reinforced polymer) is commonly used.

Can I touch fibreglass with my bare hands?

It is not recommended. Glass fibres - particularly freshly cut edges and loose fibres from rovings or fabrics - can embed in the skin and cause itching, irritation, and discomfort. Thin nitrile or latex gloves provide adequate protection for most handling tasks. If skin contact does occur, wash the affected area gently with cold water (hot water opens pores and can make removal more difficult) and avoid rubbing, which can push fibres deeper into the skin.

What do I need to keep in mind when working with fibreglass?

Several precautions make working with glass fibre safer and more effective.

• Always wear nitrile gloves to protect your hands from both glass fibres and resin systems.
• Use safety glasses or goggles when cutting or sanding.
• In dusty conditions or when machining cured laminates, wear a particle mask rated at least FFP2 or a half-face respirator with suitable filter cartridges.
• Work in a w