# Optimizing the Performance of Window Frames: A Comprehensive Review of Materials in China
## 4 Conclusions  
Improvements to windows can directly reduce their environmental impact. As a key element, window frames not only ensure the structural integrity of the window system but also play a significant role in energy efficiency and environmental conservation. In GB/T 50176-1993 [159], it is explicitly stipulated that buildings in severely cold areas and cold regions should use doors and windows with good insulation performance, such as wooden windows, plastic windows, aluminum-wood composite doors and windows, and aluminum-plastic composite doors and windows. However, in the process of selecting and using window frames, the performance of window frames is often influenced by the choice of materials, structural design, and the operating environment. This review examines commonly used window frame materials in the market, including wood, polymers, and metals. It covers the performance of different window frame materials, structural design considerations, and issues encountered during use. By considering existing improvement solutions, the review outlines the challenges that future research in this field may face. The specific conclusions are as follows:  
* Wood, as an environmentally friendly material, has minimal environmental impact throughout its life cycle. The dimensional stability of wood when exposed to water, temperature, bacteria, or weather for extended periods is a crucial consideration, given the hydrophilic and biodegradable nature of wood cellulose. Heat treatment improves wood stability against water and bacteria, but it may compromise mechanical properties due to a significant reduction in hydrogen bonds. Coating wood's outer or inner surfaces with stable polymers or inorganic materials as a stopgap measure can enhance stability without sacrificing mechanical performance. Moreover, current improvements mostly remain at the laboratory scale. Chemical enhancements to small-sized veneers (thin wood pieces, sometimes bark) and assembling them into large panels are promising directions to meet the dimensional requirements of the final product. At the current stage of using wood as a window frame material, it needs to be processed into engineered wood products. Whether focusing on the improvement of wood itself or the design of wood components, narrowing the gap between academic research and industrial practices is an essential area for future research. This will facilitate the practical application of more wood materials for the benefit of society. * Polymer materials are systems composed of a relatively large number of components; hence, the actual number of composite materials that can be realized from this array of basic elements is virtually infinite. Thermostetting composite materials exhibit excellent mechanical properties and thermal resistance at high temperatures. Composite materials reinforced with glass fibers and carbon fibers demonstrate outstanding tensile and compressive strength. Advanced composite materials are currently under research and application in various industries, such as glass fiber-reinforced polyurethane window frames. However, polymers are energy-intensive during the synthesis process and are associated with the generation of toxic gases. This impact on the environment persists throughout the entire life cycle of polymers. The heterogeneity of polymers and their difficulty in degradation make recycling both technically and economically challenging. * Aluminum alloy, known for its excellent mechanical properties and recyclability, has found increasing applications in structural engineering. This trend has prompted extensive research on the structural performance of aluminum alloys and the development of precise design methods. The production of aluminum alloys falls within the category of energy-intensive industries. The use of thermal break structures is common to enhance the thermal performance of aluminum alloy window frames. However, this often requires collaboration with insulation materials to achieve optimal thermal properties.