Skip to content
Material World
Application

Thermal insulation

Almost always trapped air or gas held still by something. The solid part is scaffolding for the void that does the work.

Nearly every insulator works the same way: a gas is a poor conductor, so a material full of small pockets of gas conducts poorly, provided the pockets are small enough to stop convection and the solid framework is thin enough not to conduct around them.

That is why the numbers cluster. Mineral wool, glass wool, expanded polystyrene, polyurethane foam and even a down jacket land within a factor of two of one another, because they are all mostly still air. Beating that range requires changing the gas — as rigid polyurethane does — or removing it, as vacuum panels and aerogels do.

Uses

Building fabric, which is the largest use by volume and the one with the greatest energy consequence; refrigeration and cold chain; industrial pipework and vessels; clothing; and cryogenic and spacecraft applications where the requirements change entirely.

Fire behaviour is the constraint that decides between them, and it is where the organic foams are weakest. The Grenfell Tower fire in 2017 turned on the combustibility of an insulated cladding system, and the regulatory response across several countries has been to restrict combustible insulation on tall buildings regardless of its thermal performance.

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.

uses

  • Polyurethane — material · rigid foam, which beats mineral wool per unit thickness because its closed cells hold a low-conductivity gas rather than air
  • Polystyrene — material · as expanded and extruded foam board — the cheapest insulation per unit of thermal resistance, and combustible, which is where the regulatory argument sits
  • Wool — material · the original, and still the reference for how a fibre traps still air
  • 6000 series aluminium alloy — alloy · as the frame of an insulating glazing unit, and a thermal break is required in the profile precisely because the aluminium conducts so well
  • Mineral wool — material · and it does not burn, which after 2017 is the property regulation cares about most on a tall building
  • Glass fibre — material · as glass wool, which is a different product from the same material and one of the highest-volume insulations there is

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Thermal insulation 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

  • Thermal insulation → uses (as expanded and extruded foam board — the cheapest insulation per unit of thermal resistance, and combustible, which is where the regulatory argument sits) → 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 brine; the salt is the feedstock for both products at once) → Halite
  • Thermal insulation → uses (rigid foam, which beats mineral wool per unit thickness because its closed cells hold a low-conductivity gas rather than air) → Polyurethane → is produced by (a diisocyanate and a polyol reacting as they are mixed, so the polymer and the finished part are made in the same moment) → 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
  • Thermal insulation → uses (as the frame of an insulating glazing unit, and a thermal break is required in the profile precisely because the aluminium conducts so well) → 6000 series aluminium alloy → is produced by (and the composition window is narrow: the magnesium-to-silicon ratio decides whether the precipitate forms usefully) → Alloying and melting → takes as input (the base metal of both brass and bronze) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Thermal insulation → uses (as glass wool, which is a different product from the same material and one of the highest-volume insulations there is) → 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
  • Thermal insulation → uses (and it does not burn, which after 2017 is the property regulation cares about most on a tall building) → Mineral wool → is sourced from (melted at around 1500 °C and flung into fibres by spinning wheels) → Basalt → is sourced from (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → Peridotite → is composed of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Olivine
  • Thermal insulation → uses (the original, and still the reference for how a fibre traps still air) → Wool

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