How basketballs are made

A basketball is an air-tight butyl rubber bladder wrapped in nylon thread and covered in pebbled leather.

stations: 8
things upstream: 64
raw sources: 20
steps from the ground: 8

The short version

A basketball has three layers. A hollow butyl rubber bladder holds the air. Nylon thread is wound round it for strength and shape, and a cover of leather or composite skin goes on top, pressed with channels and pebbles. The ball is inflated, checked and sold flat or ready to play.

Mix the butyl rubber

Butyl rubber is a synthetic polymer made of 98 percent isobutylene and 2 percent isoprene. It leaks little air and is tough enough to withstand repeated bounces.

Goes in
Synthetic rubber
Blow the bladder

Rubber is pressed into a hollow sphere with a valve opening, which will hold the air.
Wind the nylon thread

Machines wrap the bladder with nylon thread in a crisscross pattern. The windings keep the ball round when it is pumped up.

Goes in
Nylon
Cut the cover panels

Cow leather, or a composite sheet for a cheaper ball, is cut into curved panels, each with a channel pattern.

Goes in
Leather
Press the pebble texture

Heated plates emboss a fine bumpy surface on the cover panels, giving the ball its grip.
Glue the cover on

Panels are bonded to the wound bladder, leaving seam channels between them.

Goes in
Adhesive
Inflate and stamp

The ball is pumped up to playing pressure and given its logo and size markings.

Goes in
Air Ink
Bounce-test

Sample balls are dropped and checked for bounce height, roundness and air loss.

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Worth repeating

The NBA tried a composite ball in 2006-07, but after complaints from players it went back to leather midway through the season.
The NBA ball is 29.5 inches in circumference.
Basketballs range from a few inches across, for promotional items, to nearly 2 feet for training balls.