Using green façades in large cities with hot climates has been introduced in the search for more sustainable solutions for urban development. This paper presents the data collected in situ and quantifies the thermal external behaviour of a green wall and a bare one in the same surrounding environment in the city centre of Madrid, Spain. The methodological approach helps to assess the impacts of both walls on the variation of the urban temperature range at the microclimate scale in accordance with environmental physical data at different seasons and times of the day. In the summer campaign, the maximum values of air temperature reduction as measured in situ range between 2.5 °C and 2.9 °C which confirmed the values of various other studies using similar measurements. In the autumn campaign, the maximum values were half of the ones obtained for the summer, not exceeding 1.5 °C. However, these values increased after calculating similar conditions of sunlight in both façades. This comparative analysis of the experimental results on a green wall and a bare wall demonstrates that green façades can have a significant temperature reduction potential in the surrounding microclimate.