It is observed that a layered, unconfined combustible mixture supports a flame propagation velocity of 4 to 5 times the laminar flame speed of the stoichiometric mixture of fuel and air. This effect which has been observed by some and more recently in this laboratory, has never been adequately explained. It is in contrast to the classical soap bubble experiment, in which the flame propagation velocity is of the order of 7 to 8 times the laminar flame speed, that is, the order of the unburned to burned gas density ratio