5.01 This chapter considers the limits to contractual estoppel. It should come as no surprise that they are in essence the same that apply to contracts generally.1 Contractual estoppel is a creature of contract; contract at once provides the foundation for it and determines its boundaries. Where by their contract the parties create a “parallel factual or legal universe governing their relationship”,2 that universe is akin to a soap bubble, enclosed within and kept together by the film of contract. The bubble will not form unless the film is stable, and will live only so long and expand only so far as the film holds.