Key indicators: wind-load resistance — higher grade (e.g. grade 9+) resists strong wind (suited to high-rise or typhoon areas). Water tightness — resistance to rain leakage; good water tightness avoids sill leakage in storms. Air tightness — relates to insulation and soundproofing; higher grade (e.g. grade 8) means less heat loss and better soundproofing (cuts noise 30–40 dB). Insulation coefficient (K value) — lower (e.g. ≤ 1.8 W/m²·K) means stronger insulation, suited to severe-cold or hot regions.