A common cause for failure to meet specifications of packaged solid oral dosage forms (SODFs) is their instability as a result of moisture uptake during storage. Failures are usually related to out-of-specification or out-of-range values in any of the following quality attributes (alone or in combination with other physical properties): assay, related substances, degradation by-products, and dissolution rate. Therefore, the moisture barrier properties of the packaging system must be characterized properly to demonstrate the relative moisture vapor transmission rate (MVTR) performance required to protect SODFs from moisture uptake.