Thermal insulation: Rock wool and polystyrene

### Rock Wool: A High-Performance Mineral Insulator Rock wool is an insulating material made from volcanic rocks such as basalt. This material has several distinct advantages, particularly in terms of thermal performance and fire safety. From a thermal perspective, rock wool offers excellent thermal resistance, making it a popular choice for building insulation. It is characterized by its low thermal conductivity, usually between 0.033 and 0.040 W/m·K (watts per meter-kelvin), thus reducing heat loss in winter and maintaining coolness in summer. One of the remarkable properties of rock wool is its outstanding fire resistance performance. Naturally non-combustible, this material does not contribute to the spread of fires and can withstand very high temperatures, up to around 1000°C. This characteristic makes it a preferred option for constructions requiring enhanced fire safety. Rock wool is also recognized for its ability to improve the acoustics of buildings. Its dense fiber network absorbs sound waves, thus reducing noise pollution from outside or other rooms. This property is particularly useful in urban environments or in high-density buildings. However, despite its many advantages, rock wool has some notable drawbacks. For instance, it is heavier than some other insulating materials, which can complicate installation and increase labor costs. Moreover, although rock wool is water-resistant, it can lose some of its insulating properties when too damp. In terms of sustainability and environmental impact, rock wool is often considered a relatively eco-friendly option. It is made from abundant natural materials and production residues can be recycled. However, the production process requires a significant amount of energy, which can result in a considerable carbon footprint. ### Polystyrene Foam: A Lightweight and Effective Insulator Polystyrene foam is a synthetic insulating material widely used in the construction sector. There are mainly two types of polystyrene foam: expanded polystyrene foam (EPS) and extruded polystyrene foam (XPS). Each of these variants has specific characteristics that influence their specific applications. Expanded polystyrene foam is made from small polystyrene beads fused together. It is lightweight, easy to handle, and offers thermal conductivity generally between 0.030 and 0.038 W/m·K, making it effective for thermal insulation. Its main advantage lies in its lightness, allowing quicker and less costly installation compared to other materials. Extruded polystyrene foam, on the other hand, is produced by an extrusion process that creates a more homogeneous and denser cellular structure. It offers even better thermal resistance, with conductivity values often below (< 0.030 W/m·K), along with excellent compressive resistance. This increased density makes it particularly suitable for applications where high durability and mechanical resistance are required, such as flat roofs or foundations. In terms of moisture resistance, extruded polystyrene foam stands out due to its closed structure that prevents water infiltration. This makes it an ideal choice for damp environments, unlike the expanded version which can absorb more moisture, reducing its insulating efficiency. Nevertheless, polystyrene foam presents significant drawbacks, especially regarding fire safety. While some types can be treated with flame retardants, polystyrene remains a combustible material and can emit toxic fumes if ignited. From an environmental perspective, polystyrene foam also raises concerns due to its production from non-renewable petroleum derivatives and the difficulty of its recycling. Polystyrene waste can persist in the environment for a long time without degrading, posing significant waste management challenges. In summary, while polystyrene foam is efficient and cost-effective, it has limitations in terms of durability and fire safety that must be carefully evaluated when choosing this material for thermal insulation.