The conservation profession continues to debate recommended limits for environmental controls within museums. As bark paintings are considered susceptible to fluctuating environments, this study investigated the extent of movement of bark paintings from the collections of the National Gallery of Australia and National Museum of Australia over a relative humidity range likely to be encountered within museums. Forty-eight bark paintings were monitored in five storage environments for up to one year. Planar distortion of the tangential width was measured against relative humidity (RH) and temperature (T). Twenty-five percent of the bark paintings stored in a fluctuating environment (35%-63%RH) showed more than 20 mm of planar distortion. Movement was rapid and reproducible. Extent of movement should be incorporated into designs for display, transport and storage to limit damage.