Rubber is a stretchy, waterproof material that bounces back to its original shape after you squeeze, bend, or pull it. If you've ever stretched a rubber band and watched it snap back, or bounced a ball and seen it spring off the ground, you've seen rubber's defining quality: elasticity.

Natural rubber comes from the sap of rubber trees, mostly grown in tropical regions like Southeast Asia and South America. Workers make careful cuts in the tree bark, and a milky white liquid called latex drips out into collection cups. This latex gets processed into the rubber used for countless products.

The invention of vulcanization in 1839 transformed rubber from a sticky, unreliable material into something durable and useful. This process, discovered by Charles Goodyear, uses heat and sulfur to make rubber stronger and more stable. Before vulcanization, rubber products would melt in summer heat and crack in winter cold.

Today rubber appears everywhere: in car tires, shoe soles, erasers (which people sometimes call rubbers), balloons, gloves, and thousands of other products. Scientists have also created synthetic rubber in laboratories, which now makes up more than half the world's rubber supply.

The word can also mean an eraser, particularly in British English, because early erasers were made by rubbing pieces of natural rubber over pencil marks.