How office chairs are made

The height adjuster in an office chair is a sealed cylinder of compressed gas.

stations: 7
things upstream: 54
raw sources: 17
steps from the ground: 7

The short version

Plastic is injection-molded into the shell and often the five-star base, while metal bases are die-cast. Two-part polyurethane poured into a heated mold makes the cushion, and a sewn cover goes over it. Casters press into the base, a gas lift of sealed pressurized nitrogen drops into its center, and the seat sits on top.

Mold the seat shell

Molten plastic, often polypropylene or glass-filled nylon, is injected into a steel mold to make the seat and back shells.

Goes in
Polypropylene
Make the star base

A five-armed base is injection-molded from nylon, sometimes reinforced with glass fibers, or die-cast from aluminum and then machined and polished.

Goes in
Nylon Aluminum
Fill the gas lift

Gas springs are sealed cylinders holding high-pressure gas, usually nitrogen, with a piston and some oil. Pulling the lever lets gas move from one side of the piston to the other, which raises or lowers the seat. Many chair makers buy these from specialists.

Goes in
Nitrogen gas Steel
Mold the seat cushion

Two-part polyurethane is mixed and poured into a heated aluminum mold, where it expands and cures in minutes into a contoured cushion.

Goes in
Polyurethane
Cover the cushion

Fabric is cut, sewn into a cover, wrapped over the foam and glued or stapled to the underside of the seat.

Goes in
Polyester
Assemble the chair

Casters press into the arms of the base, and the gas lift drops into the center hole. The tilt mechanism is bolted under the seat and seats onto the gas lift by a tapered fit.
Test on the line

Every adjustment and wheel is checked on the line. Sample chairs go through the destructive and durability tests of the ANSI/BIFMA X5.1 standard.

End of the lineOffice chair

Worth repeating

Charles Darwin was one of the earliest known people to put wheels on a chair, to move around his study.
A swiveling chair with casters appears in a 1505 manuscript by Martin Loeffelholz von Kolberg.