Material · Synthetic

Polystyrene

Rigid, clear and brittle, and ninety-eight per cent air when foamed — the disposable cup, the packing block, and the insulation in the wall.

Insulator

Solid polystyrene is glass-clear, rigid and notably brittle — it is the plastic that cracks rather than bends, which is why a CD case snaps and a disposable fork breaks. It is cheap and easy to mould and that has kept it in production despite the brittleness.

Foamed, it is a different material entirely. Expanded polystyrene is around ninety-eight per cent air held in closed cells, and the air is what does the insulating; the polymer is just the structure holding it still. That makes it one of the cheapest effective insulators available and the standard protective packing for anything fragile.

Economic significance

Polystyrene has been losing markets steadily for decades, and mostly to polypropylene. Food containers went first, on temperature — polystyrene deforms in a dishwasher and a microwave. Then a large number of jurisdictions banned foam food service outright, on the grounds that it is nearly impossible to recycle, breaks into fragments that persist, and blows out of waste streams into watercourses.

What it retains is insulation and protective packaging, where its combination of low thermal conductivity, low cost and low weight is genuinely hard to match. Those uses are also the ones where the material stays in a building for fifty years rather than in a bin for an afternoon, which is a large part of why they survived the regulation.

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.

contains

Carbon — element · the backbone and a benzene ring hanging off every second atom, which is what makes it rigid and brittle at once
Hydrogen — element · the balance

is produced by

Polymerisation — process · straightforward addition polymerisation of styrene

is used as

Packaging — application · as expanded foam for protective packing, and formerly for food service until a great many jurisdictions banned it
Thermal insulation — application · as expanded and extruded foam board — the cheapest insulation per unit of thermal resistance, and combustible, which is where the regulatory argument sits
Protective equipment — application · the expanded foam liner of a helmet, which protects by crushing once and must then be replaced

is an alternative to

Polypropylene — material · in food containers, and it won on temperature: polystyrene deforms in a dishwasher and a microwave and polypropylene does not
ABS — material · ABS is polystyrene with a rubber phase and acrylonitrile added, and it won the durable-goods market on the toughness that gives it
Mineral wool — material · polystyrene is cheaper per unit of thermal resistance and combustible, and that trade is now largely made by regulation rather than by a designer

is sourced from

Styrene — compound · straightforward addition polymerisation

is an input to

Injection moulding — process · cheap rigid mouldings, and the reason so much disposable product was polystyrene before it was polypropylene

belongs to the group

Plastic — material · rigid and brittle, and the foam everybody pictures

Sources

Wikidata
Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
Material World
Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Polystyrene 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

Polystyrene → is produced by (straightforward addition polymerisation of styrene) → 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 the brine the cell electrolyses, and as the source of the hydrogen that comes off the cathode) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
Polystyrene → is sourced from (straightforward addition polymerisation) → Styrene → is sourced from (via ethylbenzene: ethylene alkylates benzene, and the product is dehydrogenated) → 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 → is sourced from (the fraction boiling between about 30 and 200 °C, separated by distillation rather than made) → Crude oil
Polystyrene → is produced by (straightforward addition polymerisation of styrene) → 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
Polystyrene → is sourced from (straightforward addition polymerisation) → Styrene → is produced by (by way of ethylbenzene, which is ethylene and benzene joined and then dehydrogenated) → 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 → is sourced from (the fraction boiling between about 30 and 200 °C, separated by distillation rather than made) → Crude oil
Polystyrene → is produced by (straightforward addition polymerisation of styrene) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
Polystyrene → is produced by (straightforward addition polymerisation of styrene) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite

These are the most distinct paths back. Polystyrene can be traced through others besides.

Downstream — what it becomes

Polystyrene → is used as (as expanded foam for protective packing, and formerly for food service until a great many jurisdictions banned it) → Packaging
Polystyrene → is an input to (cheap rigid mouldings, and the reason so much disposable product was polystyrene before it was polypropylene) → Injection moulding
Polystyrene → is used as (as expanded and extruded foam board — the cheapest insulation per unit of thermal resistance, and combustible, which is where the regulatory argument sits) → Thermal insulation
Polystyrene → is used as (the expanded foam liner of a helmet, which protects by crushing once and must then be replaced) → Protective equipment