An improved tiltable stool comprises a seat, a body structure, and a base. The base comprises an annular elastic base member having a downwardly convex outer surface and a downwardly concave inner surface. Deformation of the annular elastic base causes a stabilizing force which pushes the tiltable stool towards a normal position when the tiltable stool or chair is tilted out of the normal position. The stabilizing force increases with the weight of a user and provides a consistent dynamic seating experience for users of different weights. An upper section of the annular elastic base is substantially cylindrical and firmly connected to the base structure. The downwardly convex outer surface of a lower section of the annular elastic base member rests on the floor. A contact area between the annular elastic base member and the floor is substantially ring-shaped, and grows outwardly with an increasing weight placed on the seat.