Top Surface (IMAGE) Nanyang Technological University Caption The top surface of the pollen paper, which appears frosted to the naked eye, has a relatively rougher surface as compared to the bottom surface, which takes on a mirror-like surface finish. This structural difference in pollen particle layers means that in the presence of water vapour the paper starts to bend, and under dry conditions, it unbends. Repeated cycles of humid and dry conditions cause the paper to perform a flipping motion over time. Credit NTU Singapore Usage Restrictions Use with mandatory credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.