Like our ideas? Please become an FB fan of Clean Republic! Easily harness the power of the sun to heat anything inside these tubes! Even boils water after just a few hours in the sun! No moving parts. These incredible double-wall tubes have a thermos-type vacuum seal between their walls, a light absorbent coating on the outer wall of the inner tube, and three heat reflective layers on the inside surface. Sunlight and heat go in, but don't come out until you want it.