A housing is mounted to a slide that transports a series of preforms downward under the influence of gravity through a pre-heating apparatus toward a reheat blow molding machine. The housing is coupled to the slide so that a selected portion of each of the series of preforms is shielded from the general enviroment, and heating elements and directing elements are fixed within the housing so that heat from the heating elements is directed toward the selected portion of each series of preforms as the preforms desend down the slide to achieve a persistent thermal gradient in the preforms prior to the re-heating and blow-molding of the preform.