HeatSavr is most likely described in this patent which indicates that the product is just a combination of "an aliphatic alcohol component having from 12 to 24 carbon atoms per molecule" combined with calcium hydroxide. The calcium hydroxide is just a carrier and dispersing agent.

The preferred embodiment uses cetyl alcohol (1-hexadeconal) and it only takes a small amount as the layer is only one molecule thick. Another product, WaterSavr, appears to use stearyl alcohol. Yet another uses a combination of the two.

Such products only work moderately well if there is no wind. Possibly better than nothing in some cases, but no where nearly as effective as a regular solar cover.