In People & Innovations (June), you say that the Heat Mirror produced by the Southwall Corp. "reflects the sun's long, heat-producing waves" resulting in "lower energy costs in cold climates."

My firm markets many types of energy conservation and energy management products for home and industry, so we have some knowledge of heat loss/gain theory. It would seem more beneficial to allow the "heat-producing 'long' waves" in than to bounce them away in cold climates.

Can you shed some light on what seems to me a contradiction in goals?


According to the Southwall Corp., the Heat Mirror works like a thermos bottle, except that it's transparent. Though it does indeed reflect the sun's heat away from the house, it also reflects the heat being produced in the house back inside. Mounted inside a double-glazed window, the Heat Mirror film has a dead air space on either side, adding to the house's insulation. The result, Southwall claims, is a warmer house in winter and a cooler one in the summer, and a reduction in energy costs.