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Glass Fibers and Fiberglass Cloth Information

Mid-Mountain manufactures textiles designed for use as thermal seals and barriers for high temperature applications in moderate to severe environments. Glass fibers and fiberglass cloth consist of bulk, chopped fibers or continuous strands of glass. Glass fibers and fiberglass cloth is used in reinforcing plastics and composites as well as other specialized electrical and thermal applications. Fiberglass cloth is frequently used to reinforce other plastic materials. Glass fiber reinforced plastic (GRP) or glass fiber reinforced epoxy (GRE) are commonly called fiberglass.

The glass fiber used to create fiberglass material is made by extruding very thin strands of silica-based monofilament. Glass is a unique amorphous solid, meaning it doesn’t have an underlying crystalline structure in the solid state, but rather behaves like a very viscous liquid. Glass fiber lends itself to woven fabric because the thin fibers can easily bend. Fabric made of glass fibers has high tensile strength, dimensional stability, high heat and fire resistance, as well as resistance to many chemical compounds. Fiberglass fabric is also used to dissipate heat, and has electrical properties that make it useful in electronic components.

Textile Product Type 

Fiber / monofilament - Bulk chopped fibers or thin, continuous fiber filaments are used typically in composite reinforcement applications, flowable insulation or as the key component in woven fabrics, braids, knits, rope roving or other specialty fabrics.

Strands / multi-filament - Thin, continuous, multi-fiber filaments are used in composite reinforcement applications, or as the key components in woven fabrics, braids, knits, rope roving or other specialty fabrics.

Roving / yarn - Roving is made of tows, untwisted bundles of continuous filaments. Yarn is made of continuous, often plied strands of natural or man-made fibers or filaments.

Woven product - Woven products are used for composite tooling and the formation of structures. Continuous fibers are processed into two or three-dimensional structures by weaving fibers on a loom.

Nonwoven product - Nonwoven products are textile or fiber-based materials shaped into mats of randomly oriented fibers, felt, needle punched cloth, spun bound, or meltblown structures. 

Braided product - Braided products are used for tubular composite structures, thermal insulation fabrics, and in other applications.

Knitted product - Knitted products consist of continuous fibers that are processed into a knitted structure with either two or three dimensions. Knitting provides a more conformable structure than weaving, which is valuable for contoured surfaces.

Rope / cordage - Products that are made from twisted or braided rope or cordage. Heat-insulating rope or braid is used to provide a thermal seal around doors or other openings in furnace walls.

Webbing (ribbon / strap) - Products including woven ribbons, webbing, strapping or tape.

Blanket / batt - Blankets or batts (batting) are made of thick layers of woven and/or nonwoven fabric sheets.

Sleeving / wrap - Sleeves or wraps are flexible, fibrous refractory products for insulating pipes, tubes, ducts, and other process components.

Thread - Thin, continuous threads or filaments are used for stitching or reinforcement. Monofilaments are used in reinforcement applications. Multi-fiber threads are used in sewing or stitching.

Material Type

Fiberglass cloth is differentiated into two separate grades: s glass or e-glass.

E-glass - E-glass is the most inexpensive glass fiber and is used when strength and high electrical resistivity are required. S-glass is approximately 30% higher in strength than E-glass and has better properties at elevated temperatures. E-glass has high fiber strength relative to carbon and aramid (~500 Ksi), and relatively low fiber modulus (~10.5 Msi).

S-glass - S-glass® is approximately 30% higher in strength, significantly more expensive, and has better properties at elevated temperatures than E-glass. The "S" designation, a registered trademark of Owens Corning, stands for strength. Other, similar products are designated as Te-glass or R-glass.

Quartz / Fused Silica - Fused silica is a compound of silicon and oxygen. Quartz and high-purity amorphous-fused silica afford very low expansion, remarkable thermal shock resistance, low thermal conductivity, excellent electrical insulation up to 1000° C, and excellent resistance to corrosion from molten metal.

Glass fibers and fiberglass are also available in blended and coated options. Blended fibers are manufactured from a mixture of two or more different type of fibers. While coated products can be filled or sized fibers.


Dimensions and properties are important to consider when selecting glass fibers and fiberglass.


  • Fiber denier - Denier is a unit of measure for the linear mass density of fibers. It is defined as the mass in grams (g) per 9000 meters (m). Filament denier is defined as the mass per 9000 m of a single filament of fiber. Total denier is also defined as the mass per 9000 m, but applies to filament agglomerations such as yarn.
  • Fabric weight - Fabric weight is the weight per unit area of woven or non-woven fabric, textile or cloth. Overall thickness - Overall thickness is measured with a gauge that contains two flat cylinders for a relevant sample area and a spring-loaded mechanism for a consistent, applied pressure. 
  • Overall width / OD - Overall width or outer diameter (OD) is the cut width of a roll of fabric or textile material. 
  • Overall length - Fabrics and textiles are sold in roll form at varying lengths, many in excess of one mile.


  • Use temperature - Use temperature is the maximum temperature at which fibers can be used continuously, without the degradation of structural or other required end-use properties.
  • Fabric strength - Fabric strength is the load per inch-width that a fabric can withstand before breaking.
  • Breaking load (Rope / Fiber) - Breaking strength is the maximum tensile load or force that a rope, cord, webbing or fabric will hold before breaking. Breaking strength is multiplied by a safety factor to determine the actual operating or working load of the rope or textile product.
  • Thermal conductivity - Thermal conductivity is the linear heat transfer per unit area through a material for a given applied temperature gradient. Heat flux (h) = [thermal conductivity (k) ] x [temperature gradient (Δ T)]
  • Electrical resistivity - Resistivity is the longitudinal electrical resistance (ohm-cm) of a uniform rod of unit length and unit cross-sectional area. Resistivity is the inverse of conductivity.


Glass fibers and fiberglass cloth are commonly used in composite construction, including materials used in boat building. Light weight fiberglass cloth is used with a resin to produce a waterproof surface. Heavier woven fiberglass fabric can be used for greater strength and rigidity.

Glass fibers and fiberglass cloth are also used to create combination or specialty fabrics. Glass fibers and fiberglass cloth may be combined with carbon fiber or aramid fibers to make laminates and moldable fabrics for canoes, kayaks, and other high strength, low weight applications.


Glass fibers and fiberglass must adhere to certain standards and specifications to ensure proper design and functionality.

Delphi DX300340 - This specification covers the properties of a Polyamide 6, 40% glass filled, impact resistance modified injection molding grade used for the manufacture of parts that require high stiffness and toughness under extreme conditions (Example: airbag containers).

GMW15890 - This specification covers the properties of polypropylene reinforced with long glass fibers. It covers injection molding types for manufacturing of technical parts requiring high structural stiffness.

JIS C 6832 - This standard specifies the dimensions, transmission requirements, mechanical requirements, environmental requirements and the test methods of silica glass multimode optical fibers using silica glass as a core and a cladding.

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Mid-Mountain Materials, Inc.


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