This part of IEC 62788 provides a method for measuring the maximum representative change in linear dimensions of encapsulation sheet material in an unrestricted thermal exposure as might or might not be seen during photovoltaic (PV) module fabrication. The standard does not take into account any resulting stresses which may develop due to restricted dimensional changes or friction during module fabrication.

Data obtained using this method may be used by encapsulation material manufacturers for the purpose of quality control of their encapsulation material as well as for reporting in product datasheets. Data obtained using this method may be used by PV module manufacturers for the purpose of material acceptance, process development, design analysis, or failure analysis.

This method may also be used to examine other materials, such as backsheets and frontsheets as described in IEC 62788‑2. Certain details of the test (including specimen size and substrate) are specified for that application in 62788-2.