Traditionally, most glazed units were produced with an aluminum spacer. Although lightweight, durable and relatively inexpensive, this metal is very effective at conducting heat and therefore is a significant source of heat loss.
From an energy efficiency perspective, low conductivity spacers, or warm edge spacers, are a major improvement. They are made from insulating material such as foam, butyl, thermo-plastic, or thermally improved metals and therefore conduct significantly less heat energy. The result is a more energy efficient window, reduced heat loss and reduced condensation at the edges of the glazing because the glass temperature is higher. These new materials fall into the classification of Warm Edge Technology.