Damage-induced helium leakages in flexible composites are experimentally studied in this article. First, both surface and inner damage were produced in the flexible composites. Helium leakage with different damage patterns were studied based on the measurement of differential pressure. Second, the influence of damage pattern on helium leakage parameters in flexible composites was investigated. Finally, the damage-induced helium leakage mechanism in flexible composites was given. The results show that the inner damage is the main leakage source in flexible composites. [ABSTRACT FROM PUBLISHER]