Polymeric membranes/foams are often produced via phase separation. For example, by cooling a homogeneous polymer solution, a thermodynamically unstable state can be reached, at which liquid-liquid demixing into two distinct phases will occur. The polymer rich phase will constitute the membrane backbone, whereas the polymer lean phase, after solvent removal, will constitute the pores. The final morphology of the membrane is strictly related to the thermodynamic properties of the considered system, i.e. to the phase boundaries. A complete characterization of the phase behaviour of a system consists in the experimental measurement of equilibrium phases. However, this route is highly time and cost consuming: thus, the most widely used method for determining phase boundaries is the cloud point detection, i.e. the temperature at which the solution appears cloudy due to the phase separation. Although visual measurements are often carried out, the light transmittance measurements are more deterministic. Within this framework, a cloud point measurement apparatus was designed and set up. A laser diode was employed as light source, whereas a photodiode detects the transmitted light across the sample. The sample temperature control is performed via peltier cells, with the additional possibility to tune the scanning rate. The measurement of temperature and light transmittance allows one to determine accurately the cloud point temperature. The sample is cooled stepwise: the cloud point temperature is reached when the transmitted light decreases by 1% from its initial value. After the onset of demixing, further cooling will induce a further decrease in transmitted light. In this work, the PLLA-dioxane-water solution was adopted as case study system, showing that at constant polymer concentration, the dioxane/water ratio in solution highly influences the demixing temperature. The apparatus allows the exploration of various cooling protocols, useful for the investigation of temperature history influence on the detected cloud point.