| Aluminum frame | Approximately 160–205 W/(m·K) | Aluminum conducts heat readily, so an uninterrupted frame can provide a direct path between outdoor and indoor surfaces. | A low-conductivity insulating strip separates the exterior and interior aluminum sections, interrupting this direct conductive path. |
| Polyamide thermal-break strip | Approximately 0.25–0.35 W/(m·K) for unfilled polyamide | Heat still passes through the strip, but much less readily than through aluminum of the same thickness. | The strip creates a higher-resistance section in the frame. Its material, width, geometry, and connection to the aluminum all affect performance. |
| Still air | Approximately 0.024 W/(m·K) near room temperature | Still air conducts heat poorly; however, movement within a cavity and radiant exchange between surfaces can also transfer heat. | Thermal-break profiles may incorporate chambers, but cavity shape and sealing matter because air conductivity alone does not describe total heat transfer. |
| Unfilled PVC | Approximately 0.16–0.19 W/(m·K) | PVC conducts heat far less readily than aluminum, although complete window performance also depends on profile design and reinforcement. | It provides a useful material comparison: a thermal break reduces the aluminum frame’s conductive path by introducing a much less conductive section. |
| Wood, across the grain | Approximately 0.12–0.20 W/(m·K), depending on species and moisture | Wood generally conducts heat less readily than aluminum. Its conductivity varies with grain direction, density, and moisture content. | Like other low-conductivity materials, it illustrates why separating metal sections with an insulating material can limit frame heat flow. |
| Frame-to-glass edge | Depends on the glazing spacer, frame geometry, and materials | Heat can bypass the main frame path through the glazing edge and spacer, creating a localized thermal bridge. | A thermal-break frame addresses heat flow through the frame; warm-edge spacers and suitable glazing details are also important for the edge area. |
| Whole-window performance | Reported as U-factor or U-value, typically in W/(m²·K) | Whole-window heat transfer depends on the frame, glass, spacers, window size, and tested or calculated configuration. | Compare certified whole-window ratings for the specific product and glazing configuration. A thermal break alone does not determine the final U-factor. |