Abstract: The physicomechanical characteristics and microstructures of the materials are examined based on natural water immersion and freezethaw cycle by laboratory tests, and the deterioration rates are compared to investigate the deterioration characteristics of organic thermal insulation materials (polyphenolics, polyurethane, and polystyrene). The findings indicate that: (1) The water absorption curves of the thermal insulation materials display three stages of fast, gradual, and stable. The polyphenolics have the longest water absorption duration at 192 h. After 50 freezethaw cycles, the bulk water absorption rate of polystyrene is the highest, reaching 67.50%. (2) The binary linear model predicts the relationship between thermal conductivity, freezethaw cycles, and mass water/ice rate for the organic insulation materials. The rigid polystyrene and the thawed polyurethane materials are most vulnerable to freezethaw cycles. (3) The polystyrene has the lowest thermal conductivity of 0.029 1 W/(m·K) without a freezethaw cycle. However, after 50 freezethaw cycles, the thawed polystyrene and rigid polyphenolics exhibit the lowest thermal conductivities, with values of 0.034 4 W/(m·K) and 0.047 3 W/(m·K), respectively. (4) The material with the highest compressive strength, measuring 0.476 MPa is polyurethane. The performance degradation of thermal insulation of materials is mainly affected by the bubble type, pore size, and pore fracture at the microlevel.