Type IV pressure vessels are commonly used for hydrogen on-board, stationary or bulk storages. When pressurized, hydrogen permeates through the materials and solves into them. Emptying then leads to a difference of pressure at the interface between composite and liner, possibly leading to a permanent deformation of the plastic liner called “collapse” or “buckling”. This phenomenon has been studied through French funded project Colline, allowing to better understand its initiation and longterm effects. This paper presents the methodology followed, using permeation tests, hydrogen decompression tests on samples, and gas diffusion calculation in order to determine safe operating conditions, such as maximum flow rate or residual pressure level.