One embodiment provides a method of testing humidity, comprising: i) determining a property of a device which encloses a plurality of interferometric modulators and ii) determining a relative humidity value or a degree of the relative humidity inside the device based at least in part upon the determined property, wherein the determined property comprises at least one of i) the thickness and width of a seal of the device and ii) adhesive permeability of a component of the device. In one embodiment, the determined property further comprises at least one of the following: i) temperature-humidity combination inside the device, ii) a desiccant capacity inside the device and iii) a device size.