Thermal insulation: achieved through thermal-break profiles (thermal-break aluminium) and low-emissivity (Low-E) glass coatings, measured by the heat-transfer coefficient (K value) — the smaller the better. Sound insulation: mainly depends on glass thickness, layers and profile sealing, measured by sound-reduction (dB) — the higher the better. Air tightness: the ability to block air infiltration when closed, graded 1–8, higher is better. Water tightness: ability to block rain under wind and rain, graded 1–6, higher is better. Wind-load resistance: ability to stay structurally stable under strong wind, graded 1–9, higher is better.