Abstract: A chair or stool having a substantially spherical seat component. The spherical seat component is supported upon identical base support units that are designed to stack or nest within each other. Addition or subtraction of the base support units raises and lowers the chair or stool, so that the chair or stool can comfortably fit most people of different size or height. A novel mounting mechanism firmly attaches the spherical seat to the base support unit or units.

Abstract: The present invention features a chair having a large, inflated, ball-shaped seat. The ball-shaped seat of the chair re-forms in response to an individual's weight and his or her seated position. The ball-shaped seat's height is adjustable, so as to conform to differently-sized individuals. The deformable surface of the ball allows the spine of a seated individual to align itself. This activates the individual's trunk and back muscles, and makes comfortable and therapeutic seating possible for a wide variety of individuals, even those with back problems. The shell of the inflated ball can have a flexible, tough skin that is formed of rubber, plastic, leather or other air-impermeable material. For comfort and/or esthetic purposes, the shell can be covered with fabric or vinyl. Side handles can also be provided for comfort and stability. Additionally, casters can be provided for easy movement about the floor.