Methods and apparatus for detecting cross-linking in a polymer, wherein, in some exemplary implementations, the polymer may constitute an encapsulation layer for a photovoltaic module. In one example, a polymer sample is physically deformed, and sample information relating to a relaxation or a recovery of the polymer sample in response to the deformation is obtained. The sample information is then compared to reference information relating to cross-linking of the polymeric material so as to determine a degree of cross-linking in the tested polymer sample. In one aspect, such a determination of polymer cross-linking is achieved without adversely affecting a relevant functionality of the polymer/encapsulation layer (e.g., without destruction to the polymer/encapsulation layer).