This standard specifies two methods for the determination of long-term water-absorption of thermal insulation products for buildings: partial immersion and full immersion. Partial immersion is designed to simulate the water absorption of products exposed to water for a long time, while full immersion evaluates the water-absorption energy of products under specific conditions and does not directly reflect on-site use conditions. Long-term water-absorption assessments for all types of thermal insulation products for buildings are useful for assessing their Stability and long-lasting performance in humid environments.