Background and purpose — Idiopathic clubfeet are commonly treated with serial manipulation and casting, known as the Ponseti method. The use of Plaster of Paris as casting material causes both exothermic and endothermic reactions. The resulting temperature changes can create discomfort for patients. Patients and methods — In 10 patients, we used a digital thermometer with a data logger to measure below-cast temperatures to create a thermal profile of the treatment process. Results — After the anticipated temperature peak, a surprisingly large dip was observed (Tmin = 26 °C) that lasted 12 hours. Interpretation — Evaporation of excess water from a cast might be a cause for discomfort for clubfoot patients and subsequently, their caregivers.