The thermal resistance of glazing system edge-seals plays an important role in glazing system heat transfer. Highly conductive edge-seals cause excessive edge-glass energy loss and can aggravate condensation problems in cold climates. A methodology for expressing measured and calculated edge-seal conductance levels is examined. Two-dimensional simulation models for a wide range of edge-seal types are reviewed. These models were previously developed and refined on the basis of measured heat transfer data. The refined models are used to quantify limitations in the edge-seal thermal resistance measurement and subsequent data reduction. In addition, the models and information uncovered during their development are used to examine the thermal performance of an assortment of edge-seal design options that have more recently been considered for commercial introduction.KEYWORDS: double glazing, computer programs, calculating, thermal insulation, heat loss glazing, windows, seals.