The German cardinal Nicolaus Cusanus (1401-1463) proposed the determination of the humidity of air using a balance loaded with wool. Several years later the Italian architect and painter Leo Battista Alberti (1404-1472) recommended a sponge as the absorbing material. From Leonardo da Vinci (1452-1519), we have drawings of gravimetric hygrometers, equipped with either a sponge or cotton. Using an electromagnetic vacuum microbalance, we measured water vapour absorption and desorption isotherms in order to estimate whether these instruments could be used as hygrometers. Our investigations include measurements with human hair for comparison of the mass effect of the water absorption with the length variation, as used in de Saussure’s hair hygrometer.