Figure 922 Window system performance comparison Advanced Spacers

Significant improvements in spacer design have been made in the past 10-15 years. The "Swiggle Strip" spacer sandwiches a thin piece of corrugated metal between two thicker layers of butyl rubber combined with a desiccant. The conductivity is reported to be one-quarter to one-half of the conductivity of a normal aluminum spacer. Other spacers with conductivities only 6 to 11 percent as great as aluminum have been designed using silicon foam spacers with foil backing or by separating two conventional aluminum spacers with a separate strip of polyurethane foam. Future Window Enhancement Technologies

Electrochromic glass systems, referred to as "smart windows" sandwich indium tin oxide, amorphous tungsten trioxide, magnesium fluoride and gold between layers of heat-resistant Pyrex. Imposing a small voltage to the window changes its light and heat transmission characteristics, allowing radiation to be reflected in the summer and admitted in the winter.

Windows with R-values of R-16 are theoretically possible if the air or other insulating gas between window panes is replaced with a vacuum. Historically, a permanent vacuum has not been achievable due to the difficulty of forming an airtight seal around the edges of the unit. Work is presently under way on special techniques to create a leakproof seal.

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