Cell (1) for measuring the permeation of a target gas (7) through a sample (4) comprising upstream (2) and downstream (3) chambers connected by an opening (6), a primary seal (34A) in contact with the end wall (5) of the upstream chamber and surrounding the opening (6) and a removable sample holder (10) and means (32, 33) of assembling the sample holder in the cell. The sample holder comprises: - an upper frame (11) and a lower frame (15) each of which is provided with a through-opening (12); - means (24, 33) for assembling the sample in the sample holder; - a first seal (19) flush with the front face (17) of the lower frame (15) and surrounding the through-opening (16) of the lower frame (10); - in the lower frame, a second seal (20) flush with the front face (17) of the lower frame (15), surrounding the through-opening (16) of the lower frame, and surrounded by the first seal (19), and a second passageway (23) opening out between the two secondary seals (19, 20).