Abstract: A blow molding mold for making a hollow double-walled product includes male and female mold members movable toward and away from each other. The female mold member has a bottom and has first and second pairs of confronting peripheral wall segments, the wall segments of the second pair being pivotal relative to the bottom between open and closed positions. In one embodiment, the peripheral wall segments of the first pair are fixedly coupled to the bottom. In a different embodiment, the wall segments of the first pair are also pivotal between open and closed positions, and have expansion prevention walls which project outwardly from opposite sides thereof and which, when the wall segments of the first and second pairs are in their closed positions, project outwardly beyond the peripheral wall segments of the second pair.