The effect of fluctuations in relative humidity on the degradation of paper-based materials under accelerated ageing conditions has been studied in order to obtain a better understanding of environmental needs for long-term storage of paper-based archiveal materials. The rate of degradation of paper samples aged under a relative humidity ramping up and down between 40% and 60% every 12 hours at a constant temperature of 90C. Has been compared with corresponding data obtained under constant relative humidity conditions of 40% and 60%, also at 90C. Two kraft papers, an unsized waterleaf, and an alum-rosin sized paper were aged as single sheets, or between plexiglass sheets in piles, in order to simulate a book. For single sheets ageing under cycling conditions produced similar deterioration as constant conditions. For samples aged as simulated books, the damping effect due to increased paper mass helped slow down deterioration induces by cycling conditions, but test samples inside simulated books inevitably aged faster than single sheets, possibly due to trapped degradation products.