Humidity and temperature can vary across the world. For this reason, during storage and processing, batches of the same powder may interact with diverse environmental conditions and eventually vary in their properties. For example, a higher atmospheric water vapour content could increase the water adsorbed on the surface of individual powder particles. This adsorbed water can alter the surface interactions between particles, affecting its flow behaviour. In this study, we measured the flow behaviour of various sieve fractions and steel powders in different environmental conditions. We set the environmental conditions in a C1000-40 climate chamber to different levels of relative humidity and temperature. The powder samples and a Freeman FT4 powder rheometer were placed in the climate chamber and equilibrated for 72h. Subsequently, we tested the flow behaviour using two different programs of the powder rheometer. Ultimately, we found that powder flowability is adversely affected by increased humidity.