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Selection of insulation materials for corrosion under insulation (CUI). The insulation layer acts as a pathway for the diffusion of water and electrolytes; choosing appropriate insulation materials can effectively reduce the impact of CUI. Insulation materials are divided into two main categories: hydrophilic and hydrophobic. Hydrophobic insulation materials include those that are inherently hydrophobic (such as foam glass) and those that become hydrophobic after the addition of chemical additives (such as WRG rock wool). Commonly used hydrophilic materials include rock wool and calcium silicate. Engineering practice shows that water-absorbing materials accelerate the CUI rate ； Insulation materials with a fast drying rate and low moisture content can effectively reduce CUI. When selecting insulation materials, factors such as cost, thermal conductivity, temperature limits for use, compressive strength, and construction feasibility should also be taken into consideration. No insulation material can prevent the occurrence of CUI, mainly due to: ① the structure of the protective layer. There must be openings in the protective layer, and there must be gaps between the insulation material and the metal surface, providing pathways for water and corrosive agents to enter and exit ； ②It is determined by the composition of the insulation material itself. Insulation materials possess wettability, water solubility, and permeability ； ③The insulation material itself contains pollutants; when it becomes damp or wet, these pollutants seep out of the insulation material and spread toward the metal surface along with the moisture.