Nike's Air Jordan shoes weigh about 15 ounces each. Reebok's Pump weighs 22. But the important ingredient in these two hot basketball shoes is virtually weightless. It's Reebok's air and Nike's gas. First it was sneaker wars, now air wars. The battle of the voids.

The two giants in the athletic shoe business enter the 1990s with dueling technologies, including inflatable bladders and compressed-gas pockets tucked inside their basketball shoes. All this, when not so long ago the sneaker was just a few slabs of rubber attached to canvas.