Drying is a critical step during the processing of cellulosic materials, but despite that, molecular scale structural changes during this process are not yet fully understood. Water will remain present even in seemingly completely dry materials, sorbed to specific sorption sites inside of pores[1]. It has previously been shown that the presence of water on the fibril-fibril interfaces inside cellulose fibril aggregates is thermodynamically favourable[2]. The objective of this study is to investigate the properties of this confined water, to help answer what role it has; and how the system changes during drying, when even the last water molecules are removed.This study uses all-atom molecular dynamics simulations of systems comprised of a thin layer of water between infinitely large sheets of crystalline cellulose, as well as simulations of a model fibril aggregate to study cellulose-water interactions on the molecular scale. Between the simulations, the distance between the confining cellulose planes is varied. Equilibrium simulations are combined with simulations of stepwise dehydration, where water is gradually removed. The analysis of these simulations focuses on investigation of the properties of the water inside of cellulose fibril aggregates.Results show that water confined in cellulose has lower molecular mobility than bulk water as a consequence of a combination of confinement and interfacial effects. Furthermore, the formation of periodic ordering in the water on top of the cellulose surface is revealed, which is connected to structural features of the cellulose fibril. These structures can be quantified and compared by defining a spatial order parameter. Simulations of continous dehydration uncover anomalous behaviour in the remaining water layer, as well as the development of hydration forces at play during this process. An analysis of the thermodynamics alongside this characterisation provides information on the precise changes in the enthalpy and entropy of the hydrated cellulose system.