611-2105 Reverse Density Rod: Everyone knows water gets less dense as it gets warmer. Then why does this rod sink in cold yet float in less dense hot water? The answer lies in the fact that the density of the rod also changes with temperature. The rod becomes much less dense at higher temperatures. It wins the “race” against the heated water and floats, whereas the aluminum rod sinks.Contains: High-density polyethylene plastic rod, 1/2” in diameter, weighted and tested; instructions with theory.