A ball chair is a specific design of chair invented by Finnish designer Eero Aarnio. It first became prevalent in the early 1960s and increased in popularity from there, though its unconventional eggshell shape fell out of favor with most homeowners are popular styles changed. The ball chair can be eggshell-shaped or completely round; the earliest models were completely round, and they were sometimes known as globe chairs. The inside of the ball or globe was upholstered and cushioned for comfort, and a person sitting inside the chair could find several different comfortable sitting positions easily.
The shell of the ball chair was originally made of fiberglass, and most models today are still made from this material or from acrylic. Fiberglass combined with the upholstery inside the chair can lead to a soundproof environment, and one of the selling points of the chair was one's ability to take a private phone call within the chair, even if others were in the room. Some modern versions of the ball chair feature stereo systems or mp3 capabilities, further enhancing the comfort and convenience capabilities of this oddly shaped chair.
The round part of the chair is mounted to a solid base, which often allows the round chair to swivel. The swiveling feature allows a person siting inside the ball chair to face other directions, thereby making interactions with other people possible. Some variations of the chair feature a cut-off top so the person sitting in the chair is not completely isolated; only the bottom of the ball exists, so this is not a true ball chair but only a design based off the original. More modern designs are usually larger than the original to accommodate taller persons and to make the unit more comfortable in general. The design of the chair accommodates for the need to move the chair through doorways as well.
While not specifically designed for this purpose, a ball chair is useful for maintaining heat, since one's body heat is less likely to escape the semi-enclosed sitting space than it would be if a person was sitting in a more conventional chair. The sides and top of the chair are upholstered, further adding to its heat retention abilities. If facing toward a stove or fireplace, the ball chair can capture and contain heat from the heat source and retain it within the chair for added comfort.