How polyurethane is made

Polyurethane foam in a couch is a chemical reaction that happens in seconds and puffs up like bread dough.

stations: 6
things upstream: 13
raw sources: 6
steps from the ground: 4

The short version

Polyurethane is made by reacting two liquids, a polyol and an isocyanate. Metering pumps send them to a mixing head with catalysts and a little water or gas. The mixture foams and rises as it cures. On a long conveyor it forms a continuous block, which is cut into cushion shapes.

Make the polyol

Propylene is converted to propylene oxide, which is built up into long, flexible chains with a hydroxyl group at each end. These are the polyols.

Goes in
Propylene
Make the isocyanate

Nitric acid and a chlorine-based reagent are used to convert aromatic petrochemicals into isocyanates in closed plants with strict safety controls. These are the reactive partners of the polyol.

Goes in
Nitric acid Chlorine
Meter and mix the streams

High-pressure pumps measure the polyol, the isocyanate, a catalyst, a surfactant and a small amount of water into a mixing head. Proportions decide whether the foam is soft or rigid.

Goes in
Water
Pour and let it rise

Poured onto a moving conveyor, the mix begins to react at once. Water makes carbon dioxide bubbles that inflate the foam as the polymer sets around them.
Cure the foam block

The block, sometimes several meters across, is left to finish reacting and cool. Heat from the reaction runs through it for hours.
Slice and shape it

Blades slice the block into sheets for mattresses and cushions. Rigid foam for insulation panels is made by similar reactions.

End of the linePolyurethane Next it goes into adhesive bandage, pacemaker, adhesive and 23 more.

Worth repeating

Foams are the largest use of polyurethane, accounting for 67% of all of it in 2016.
Otto Bayer and his team at IG Farben in Leverkusen first made polyurethanes in 1937.
Global polyurethane production in 2019 was 25 million metric tonnes, about 6% of all polymers.