Actually, the first time I saw the concept it wasn't piezo, it was an insole with a fluid-filled flat hourglass shape and a tiny turbine in the bottleneck. That was a LONG time ago.<br><br>I can't imagine battery-heated clothing becoming popular even if the cells themselves make some huge strides in efficiencey and weight reduction- and if they did, I would tend to think that would work against another source of portable energy in the marketplace, not for it. At one point I thought wearable computers might stimulate development of alternative portable energy sources, but we've now reached a point where practically everyone is carrying a battery-powered phone, and there's still almost no interest.<br>