# Mycelium-Based Thermal Insulation for Domestic Cooling Footprint Reduction: A Review
## 5 Conventional Insulation Materials
### Organic Insulation Material
#### 5.2.1 Petrochemical Insulation Material  
Polystyrene is derived from styrene, an aromatic hydrocarbon obtained by reacting ethylene with benzene in aluminum chloride. Styrene is then polymerized using free-radical initiators to form polystyrene, a synthetic polymer with the chemical formula (C8H8)\({}_{\text{n}}\). Polystyrene can be solid or foamed and can be copolymerized or blended with other polymers to produce different types of products [50], such as solid plastic which includes general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). GPPS is clear, hard, and brittle, while HIPS is opaque, tough, and impact resistant. Both types are easy to process and have a variety of applications, such as packaging, containers, toys, and models [51]. Foam includes EPS and XPS. EPS is a lightweight, durable material with excellent thermal insulation. EPS is made from polystyrene beads that are expanded by steam and molded into blocks or boards. XPS is an insulation material made from plastic beads that are melted and extruded into a continuous foam sheet. XPS has a smooth surface and a closed-cell structure, making it resistant to water and moisture. Both types of foam have low thermal conductivity and are often used for insulating roofs, walls, floors, and foundations [51]. Film: This includes oriented polystyrene (OPS), a thin, transparent film that can be stretched or oriented in different directions. OPS has good clarity, stiffness, and strength and is often used for packaging food and other products [51].  
Polyurethane comprises a category of polymers formed by linking organic units through carbamate (urethane) connections. Polyurethane can be produced from a wide range of starting materials and has many different applications, including foams, varnishes, coatings, adhesives, electrical potting compounds, and fibers. As a common procedure, polyurethane is generated through the reaction between an isocyanate and a polyol compound. Isocyanate is a compound that contains two isocyanate groups (-NCO), which can react with hydroxyl groups (-OH) from polyols. Polyols are compounds that contain multiple hydroxyl groups, such as glycols, polyesters, or polyethers [52]. It has high thermal insulation properties, which can reduce heat loss and carbon emissions. It also blocks air and moisture, acting as a barrier to leaks. It can be utilized in high-pressure or low-pressure foam and open-cell or closed-cell foam configurations. Polyurethane insulation's advantages are its versatility, light weight, durability, and easy installation. It can be used for various applications, such as roofs, walls, floors, and prefabricated panels. It can also be sprayed onto almost any surface, including complex interior spaces [53]. Some of the limitations of polyurethane insulation are its flammability and smoke emissions. Polyurethane can catch fire easily and produce toxic fumes when burned. Therefore, it needs to be protected by fire-resistant materials or coatings. Polyurethane may also degrade over time due to exposure to UV rays, moisture, or chemicals. Therefore, it needs to be inspected and maintained regularly. Polyurethane's environmental effects may stem from its reliance on fossil fuels and emissions of greenhouse gases during both its manufacturing and disposal processes [54].