Determining a barrier effect of a coating for a medium includes: providing a substrate having the coating on its surface, the substrate undergoing a volume change on contact with the medium; conditioning the substrate with the coating; removing the coating from a first part of the surface, leaving the coating on a second part, the first part having an extent in a first direction delimited by the coating remaining on the second; determining a height profile of the coating on the second part and the first part on a path in the first direction; exposing the remaining coating and the first part to the medium; determining a second height profile of the coating on the second part and the first part on the path in the first direction and/or determining a difference in height profile on the second and first part with respect to the height profile determined beforehand.