A chamber is normally made by filling a large cylinder with a liquid heated to just below its boiling point.
Charged particles create an ionization track, around which the liquid vaporizes, forming microscopic bubbles.
Bubble density around a track is proportional to a particle's energy loss.
Bubbles grow in size as the chamber expands, until they are large enough to be seen or photographed.
Several cameras are mounted around it, allowing a three-dimensional image of an event to be captured.