Structural glass bonding makes wood–aluminium windows competitive. For many decades, wooden windows have been losing market share to plastic windows. Long-term use of wooden windows incurs high maintenance costs. Periodic painting is necessary to protect the windows against rotting. Exterior aluminium shells provide natural weather protection, which explains the increasing popularity of wood–aluminium windows. They have higher costs than plastic or wooden windows. Consequently, wood–aluminium windows are designated as premium windows. In wooden windows, bonding technology utilises the glass to provide natural weather protection. The glass covers the sash frame frames and thus protects them. This saves time and material.