How is the theme of isolation developed within The Bell Jar?

A sense of confinement permeates Plath's novel, even as represented by the bell jar that forms the title of the book. The bell jar symbolizes Esther's suffocation, for the jar intends to preserve its ornamental contents but instead traps them in stale air. Plath includes several instances in which Esther imagines herself as confined, including when she compares herself to a character in a short story and imagines herself trapped up in a tree unable to decide which fig (each representing a different career path) to choose. Even the place where Esther is found after her suicide attempt represents this sense of confinement; Esther is found essentially holed up in her basement. However, this is the only instance in the novel that finds Esther literally trapped; the other instances in which this theme appears are allegorical, demonstrating that Esther's sense of confinement is largely mental. The sense that she is trapped is the most obvious manifestation of her mental illness.