The formation of a single soap film from a liquid reservoir raises a question about the origin of the additional surfactant molecules needed to coat the newly created surface. We have thus studied films made from insoluble surfactants (sodium decanoate and sodium octanoate) and varied the pH to monitor the solubility and possibly the exchange of surfactants between surface and bulk. We show that there exists a pH range where the foaming is optimum; the film formation then obeys the Frankel law, but with some discrepancy at high pulling velocities that we may attribute to the breakage of the surfactant wall and the loss of elasticity.