Material · Synthetic

Glass fibre composite

Glass fibre in a resin — the boat hull, the wind turbine blade and the water tank, and the composite everything else is compared against on price.

A glass fibre composite is fibres carrying the load and a resin holding them in place, transferring load between them and stopping them buckling. Neither component is any good alone: the fibres are a bundle of threads and the resin is a brittle solid, and together they are a structural material.

It is the workhorse. More composite is made this way than by every other route combined, because it is cheap, easy to lay up by hand, and strong enough for a very wide range of things.

What cannot be quoted for it is a single strength. A laminate's properties belong to the lay-up rather than to the material — the same fibre and resin give a stiff panel or a flexible one depending on how the plies are oriented, and a unidirectional test coupon and a chopped-strand moulding differ by a factor of several. Anyone quoting one number for 'fibreglass' is describing a particular laminate.

Processing

Hand lay-up and spray-up for hulls and one-offs, which needs little equipment and depends heavily on the operator. Vacuum infusion, which draws resin through dry fabric under vacuum and gives a much better and more consistent fibre fraction. Filament winding for pipes and pressure vessels. Pultrusion for constant sections. Compression moulding of sheet moulding compound for volume automotive parts.

Most of it uses unsaturated polyester resin, which is cheap and cures at room temperature and is what a boatyard smells of. Epoxy is used where the performance justifies the cost.

Uses

Boat hulls, which is where the material established itself and where it displaced wood almost completely in a couple of decades. Wind turbine blades, which are the largest composite structures made. Water and chemical tanks, pipes and ducting. Vehicle body panels and truck bodies. Building panels, roofing and cladding. Circuit board substrate, as glass fabric in epoxy.

Bathtubs, shower trays and swimming pools, where the surface is a gel coat and the structure behind it is laminate.

History

Boat hulls from the 1940s, and the change was rapid and complete: a wooden hull needs skilled labour, seasoning, caulking and continual maintenance, and a moulded one needs a mould and unskilled labour. Small-boat construction has not gone back.

Environmental impact

This is the composite industry's standing problem and it has no good answer yet. A cured thermoset laminate cannot be melted or separated into its components; grinding gives filler, pyrolysis gives shortened fibres worth less than new ones, and co-processing in a cement kiln — where the glass becomes feedstock and the resin becomes fuel — is the best current route and is not recycling.

The first large cohort of wind turbine blades is now retiring, which has made a problem that was theoretical for decades into a visible one. Cleavable resin chemistries and thermoplastic matrices are in development for exactly this, and none is standard.

Against that: a GRP hull or tank routinely lasts forty years with almost no maintenance, and durability is a real environmental property that is easy to leave out when only end of life is counted.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is composed of

Glass fibre — material · the reinforcement, and the fibre's strength is not the laminate's
Epoxy resin — material · or, more often and more cheaply, an unsaturated polyester resin

is used as

Structural engineering — application · hulls, tanks and blades — the cheap composite that everything else is compared against

is used in

Energy generation — industry · wind turbine blades, the largest composite structures made and the ones now retiring without a route
Shipbuilding — industry · small craft almost entirely, since a moulded hull needs a mould and unskilled labour where a wooden one needs skill and maintenance
Printed circuit board — object · the FR-4 laminate itself: woven glass cloth in flame-retardant epoxy, stiff, dimensionally stable when heated, and self-extinguishing
Smartphone — object · the board everything else is mounted on, which is a thermoset and therefore the part of the phone that most reliably becomes waste

is an alternative to

Carbon fibre composite — material · five times the stiffness at 80 per cent of the weight, and perhaps ten times the price — which is why a hull is glass and a wing is carbon

is commonly confused with

Glass fibre — material · 'fibreglass' means the fibre to a manufacturer and the composite to everybody else, and the two have entirely different properties

succeeded

Wood — material · in small boat construction, and completely: a moulded hull needs a mould and unskilled labour where a wooden one needs skill and continual maintenance

is used to make

Printed circuit board — object · which is by a wide margin the largest use of glass fibre composite by number of parts, and the one nobody counts as a composite application

is produced by

Heat treatment — process · the same, and mostly without the autoclave, which is why it costs a fraction as much

Sources

Material World
Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Glass fibre composite back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Glass fibre composite → is composed of (or, more often and more cheaply, an unsaturated polyester resin) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
Glass fibre composite → is produced by (the same, and mostly without the autoclave, which is why it costs a fraction as much) → Heat treatment → takes as input (and the same steel becomes a spring, a cutting edge or a machinable bar depending only on the schedule) → Steel → is composed of → Iron → is produced by (as pig iron, high in carbon and brittle until refined) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
Glass fibre composite → is composed of (the reinforcement, and the fibre's strength is not the laminate's) → Glass fibre → is produced by (drawn through a bushing of hundreds of platinum-alloy holes, at a diameter of a few micrometres and a speed of tens of metres a second) → Glass melting → takes as input (as the stabiliser, and without it a soda-silica glass would slowly dissolve in water) → Limestone → is sourced from (precipitated from it, mostly by organisms building shells and skeletons out of dissolved calcium and carbonate) → Seawater → is composed of (about 96.5 per cent by mass — seawater is 3.5 per cent dissolved solids and the rest of it is this) → Water
Glass fibre composite → is composed of (the reinforcement, and the fibre's strength is not the laminate's) → Glass fibre → is sourced from (as silica sand, with limestone and clay for the rest of the E-glass batch) → Quartz
Glass fibre composite → is composed of (or, more often and more cheaply, an unsaturated polyester resin) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
Glass fibre composite → is composed of (or, more often and more cheaply, an unsaturated polyester resin) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (into polyethylene, and via ethylene dichloride into PVC — the two highest-tonnage plastics between them) → Ethylene → is produced by (the principal product, and the largest-tonnage organic chemical made anywhere) → Steam cracking → takes as input (the European and Asian cracker feed; North American crackers mostly run on ethane from natural gas instead, and make a different product slate as a result) → Naphtha

These are the most distinct paths back. Glass fibre composite can be traced through others besides.

Downstream — what it becomes

Glass fibre composite → is used in (the FR-4 laminate itself: woven glass cloth in flame-retardant epoxy, stiff, dimensionally stable when heated, and self-extinguishing) → Printed circuit board → is used in (and it is the change that made electronics manufacturable: assembly stopped being a wiring job and became a printing one) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
Glass fibre composite → is used in (the board everything else is mounted on, which is a thermoset and therefore the part of the phone that most reliably becomes waste) → Smartphone → is used in (and it is where four separate raw-material arguments meet — the 3TG conflict minerals, cobalt, the rare earths, and everything too dispersed to recover) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
Glass fibre composite → is used as (hulls, tanks and blades — the cheap composite that everything else is compared against) → Structural engineering
Glass fibre composite → is used in (wind turbine blades, the largest composite structures made and the ones now retiring without a route) → Energy generation
Glass fibre composite → is used in (small craft almost entirely, since a moulded hull needs a mould and unskilled labour where a wooden one needs skill and maintenance) → Shipbuilding
Glass fibre composite → is used in (the board everything else is mounted on, which is a thermoset and therefore the part of the phone that most reliably becomes waste) → Smartphone → is associated with (the object the whole period arrives at, and the one that put roughly sixty elements into a pocket) → The semiconductor era complete chain

These are the most distinct paths onward. Glass fibre composite ends up in others besides.