No significant plastic deformation prior to the yield point of the beads was found from the profiles in Fig. 1, irrespective of the relative humidity. However, the relative humidity had a significant influence on the fracture pattern of beads as seen in the post-peak regions of the stress–strain profiles. The fracture behavior of individual coated beads was also significantly changed by the storage humidity. The SEM photographs demonstrated a brittle fracture behavior for coated beads that were stored at 0% RH for 5 weeks, as shown in Fig. 2A. The beads stored at 0% RH generally demonstrated a sharp decline in stress after the coated beads were fractured. The beads split into several fragments at the stress of fracture and a few large fragments remained on the lower platen of the Chatillon® gauge. Thus, no residual stress was detected. However, the coated beads stored at 84% RH showed ductile behavior, as seen in Fig. 2B, where the beads flattened to a plate-like shape after fracturing. Since the mobility of molecules determines the ductility of a material, the moisture was shown to change the mobility of the polymeric chains due to the uptake of water into the polymeric film. The transition from a brittle fracture behavior to ductile behavior was found to take place at 51% RH (Fig. 2C). The brittle-to-ductile transition of the coated beads resulted from a hydroplasticization effect on the acrylic polymer due to the uptake of moisture by the plasticizer. When moisture was removed, the coated beads demonstrated a brittle fracture pattern.