It is a common assumption that the microclimate inside archival boxes is very stable due to the presence of large amount of hygroscopic material (paper) inside a small air volume. However, we show how the relative humidity and temperature actually fluctuated widely inside archival boxes made from corrugated cardboard, and filled with paper, when the ambient air was forced to sudden cycles of increasing intensity in relative humidity (RH) or temperature in a climate chamber. For ambient fluctuations of ±12% RH (over 24 h) at constant temperature the inside air space of a box experienced RH changes of ±8% RH during the same time period. A sudden 4 K increase in room temperature was retarded so that the box’s air experienced the same increase only after 8 h, however, the first 1 K increase happened after only 22 min, 2 K after 42 min, and 3 K after 1 h 34 min. The transparency of the cardboard to moisture transport cause a low climate stability inside the boxes, despite the large reservoir of moisture which is available for humidity buffering inside such a box full of paper.