When retrofitting container units, the choice of insulation material directly impacts living comfort and energy consumption. Three mainstream materials—EPS (expanded polystyrene foam), PU (rigid polyurethane foam), and rock wool—each possess distinct characteristics.
EPS (expanded polystyrene foam) is the most affordable and lightweight option; it is easy to install, and its closed-cell structure ensures stable thermal insulation. However, its critical weakness is flammability—it releases toxic black smoke when exposed to fire—and its low structural strength makes it prone to deformation under long-term pressure. It is suitable for temporary worker shelters where budgets are tight and fire safety requirements are not stringent.
PU (rigid polyurethane foam) offers the best overall performance. It has the lowest thermal conductivity (approximately 0.022 W/m·K), providing far superior insulation compared to EPS or rock wool at the same thickness. It can be spray-applied on-site to seamlessly fill gaps, effectively eliminating thermal bridging. Additionally, PU boasts high compressive strength and strong adhesion. Its downsides include high costs and flammability; it releases highly toxic cyanide gas when burning, and while flame retardants can be added, the fire risk cannot be entirely eliminated.
Rock wool’s standout advantage is its Class A non-combustibility; capable of withstanding temperatures exceeding 1,000°C, it is the top choice for fire safety. It offers excellent vapor permeability—helping to regulate indoor humidity—and superior sound insulation. However, it has a high water absorption rate, causing thermal performance to plummet when damp. Its fibrous structure results in low strength and a tendency to delaminate or sag over time. Installation requires full protective gear to prevent skin irritation, making the process less efficient.
Overall recommendation: If maximizing energy efficiency is the goal and the budget allows, choose PU, but ensure a fire suppression system is installed. If fire safety is the top priority (e.g., for residential containers), rock wool is the most reliable choice, provided proper moisture barriers and external securing methods are used. For short-term use, EPS offers the best cost-performance ratio. In practice, a "PU + rock wool" composite solution is often employed—using an inner layer of PU for thermal insulation and an outer layer of rock wool for fire safety—to leverage the strengths of both. There is no single "best" material; the "most suitable" choice depends on balancing intended use, cost, and safety requirements.
