Ethylene vinyl acetate (EVA) is commonly used as the encapsulant in the manufacture of solar modules. To withstand harsh environmental conditions, EVA must be cured in properly thermal treatment. This paper will present and discuss heat treatment of EVA and the extent to which EVA is cured (gel content) using heat treatment, and its correlation to solubility and differential scanning c~lorimeter (DSC) curves. Based on the correlation between the DSC and solubility techniques performed on a given EVA, the treatment needed to obtain sufficient curing can be deduced. EVA must be at least 80 percent cured to be acceptable for making solar modules, thermal treatment in the curing of EVA (ICC 105) must be done at 140 -150°C with a curing time of 10-20 minutes.