The relationship between the size of films in a dry foam and the size of the bubbles is investigated. The study was carried out using foam structures simulated using Surface Evolver, with the structures covering a wide range of poly-dispersities. It was found that the most important factor influencing the size of a film is the size of the smaller bubble to which it is attached. The larger bubble does have an influence, but it is much smaller, with the film size increasing by approximately 80% as the larger bubble goes from the same size as the smaller bubble to infinitely large. The relationship between a film's size and the size of the two bubbles to which it is attached was found to be independent of the underlying bubble size distribution, with the probability distribution for the size of the film depending only on the size of the neighbouring bubbles.