‘Arctic’ Windows are not technically a style of window, but more a categorization of product design and analysis, dedicated to meeting requirements for superior thermal characteristics for the building’s fenestration. Our designs are custom-engineered and analyzed to enhance the insulating values and condensation resistance of the products. Heat-loss, normally measured by U-value and its reciprocal R-factor, is primarily determined by the glazing chosen. Insulating glass options include low-emissivity coatings (varying performance characteristics) and gas filling with argon or krypton. The insulating characteristics of the members (perimeter framing and mullions) plus the glazing spacers are the primary determinants of a window or curtain wall’s condensation resistance. In certain environments (e.g. a hospital with high interior humidity in a cold climate), it is critical to minimize condensation, in order to mitigate growth of mould and other pathogens. Condensation resistance is a measurement of energy transfer from the exterior to the interior of a building. By super-insulating window and curtain wall members, combined with appropriately high-performing glazing, ‘Arctic’ designs raise interior surface temperatures. This minimizes or eliminates condensation. Relative humidity and ambient temperatures are key factors in determining the likelihood of condensation. In all cases, architects must consider additional means of avoiding condensation, including humidity control, increased air-flow around the windows or curtain wall, etc. Within the ‘Arctic’ design philosophy is a subtle interplay between U-values of glazing and condensation resistance. The relationship is minimal at the center of the glass, but is can be significant at glass perimeters, and more pronounced again when mullion spacing and glass lites are small. Computer-aided design is integral to the quality of an ‘Arctic’ system. We use advanced thermal simulation techniques, often combined with project-specific physical testing, to ensure that the client’s needs for a healthy and energy-efficient building are met.