Selecting the correct PU injection material depends on the intended use, such as waterproofing, structural reinforcement, or component manufacturing. For leak sealing, prioritize hydrophilic resins which expand upon contact with water. For structural lifting or void filling, hydrophobic closed-cell foams are superior due to their high compressive strength and stability. Always verify the expansion ratio (typically 10x to 30x) and curing time to ensure it meets your project's specific timeline and environmental conditions.