Method for measuring the leaktightness of sealed containers

An in-procces control method in a production run of an on-going packaging process for pharmaceutical formulations to test the leaktightness of a sealed container that holds a pharmaceutical active substance formulation in a chamber, the method comprising the steps of:

• a) acting upon the sealed container with a gas such that any increase of the gas inside the chamber can be analyzed;
• b) removing a sample from the chamber;
• and c) analyzing the sample for the presence of the gas, wherein the sealed container is a sealed, two-layer, container with a rigid outer shell and an inner container mechanically attached to the outer shell only at certain points and able to collapse in on itself relative to the outer container.