In this work, the fundamentals and the limitations of the Fanger's comfort model were presented, in particular the one concerning the evaluation of the metabolic rate. As emerging from recent researches, the use of wearable sensors capable of measuring physiological parameters can help overcome the analyzed drawbacks. A new framework for the description and classification of such wearable sensors was proposed, based on a critical review of recent studies that have already experimented their use for the purpose of thermal comfort evaluation. It was finally discussed how these devices are able to improve the estimation of thermal comfort conditions and the extent to which they can better explain subject preferences.