Fiberglass

Fiberglass (also spelled fibreglass) is a type of fiber-reinforced plastic that uses glass fiber. The glass fibers can be arranged randomly, pressed into a mat (chopped strand mat), or woven into cloth. The plastic part is usually a thermoset polymer like epoxy, polyester, or vinyl ester resin, though thermoplastics are also used. It costs less and is more flexible than carbon fiber, and it’s stronger than many metals when compared by weight. It doesn’t conduct electricity or magnetism, lets electromagnetic radiation pass through, can be shaped into complex forms, and resists chemical reactions in many conditions. It’s used in things like aircraft, boats, cars, bathtubs, swimming pools, hot tubs, septic tanks, water tanks, roofing, pipes, cladding, orthopedic casts, surfboards, and door skins. Other names include glass-reinforced plastic (GRP), glass-fiber reinforced plastic (GFRP), or GFK. Since the glass fiber itself is sometimes called “fiberglass,” the full composite is also called fiberglass-reinforced plastic (FRP). Here, “fiberglass” refers to the whole composite, not just the glass fiber inside.

Glass fibers have been made for centuries, but the first U.S. patent went to Prussian inventor Hermann Hammesfahr in 1880. Mass production of glass strands happened by accident in 1932, when Owens-Illinois researcher Games Slayter shot compressed air at molten glass and created fibers. A patent for that method (making glass wool) was filed in 1933. Owens joined Corning in 1935, and by 1936 Owens Corning had adapted the method to produce its patented “Fiberglas” (spelled with one “s”). That original Fiberglas was a glass wool full of trapped gas, useful as insulation, especially at high temperatures. In 1936, DuPont developed a suitable resin to combine fiberglass with plastic. The first modern polyester resin came from Cyanamid in 1942, using peroxide curing systems. When fiberglass and resin were combined, the gas was replaced by plastic, lowering insulation to typical plastic levels but giving the composite great strength for structural use. Many glass fiber composites kept the name “fiberglass,” which also still referred to the low-density glass wool product. Ray Greene of Owens Corning built the first composite boat in 1937 but stopped because the plastic was too brittle. In 1939, the Soviet Union reportedly made a passenger boat from plastic, and the U.S. built an aircraft fuselage and wings. The first car with a fiberglass body was a 1946 Stout Scarab prototype, but it never went into production.

For strong structural fiber, the glass fiber surfaces must be nearly defect-free to reach gigapascal tensile strengths. A defect-free bulk piece of glass would be just as strong, but making and keeping it that way outside a lab is impractical.

The manufacturing process for fiberglass is called pultrusion. To make reinforcement fibers, large furnaces melt silica sand, limestone, kaolin, fluorspar, colemanite, dolomite, and other minerals into a liquid. This liquid is extruded through bushings (spinnerets) with tiny holes—typically 5–25 micrometers wide for E-Glass, 9 micrometers for S-Glass. The filaments are then coated with a chemical sizing. Many filaments are bundled into a roving. The roving’s weight is measured in yield (yards per pound; a smaller number means heavier roving, e.g., 225, 450, 675 yield) or tex (grams per kilometer; a smaller number means lighter roving, e.g., 750, 1100, 2200 tex). Rovings can be used directly in pultrusion, filament winding (for pipes), or gun roving (where a gun chops glass into short lengths and sprays it with resin onto a mold). They can also be made into fabrics like chopped strand mat (CSM), woven, knit, or unidirectional fabrics.

Chopped strand mat (CSM) has glass fibers laid randomly and held together by a binder. It’s usually processed by hand lay-up: sheets are placed on a mold and brushed with resin. The binder dissolves in the resin, letting the mat conform to shapes when wet. After the resin cures, the hardened product is removed from the mold and finished. CSM gives fiberglass isotropic in-plane properties.

A coating or primer (sizing) is applied to the roving to protect the glass filaments during handling and to ensure they bond properly to the resin matrix.