The accessibility of the cellulose in wood pulps to solvents and reactive agents is usually limited. Only the cellulose molecules on the surfaces of the fibrils or fibril aggregates as well as between the crystallites in the cell walls are accessible. Aggregation of the cellulose fibrils can also render the amorphous cellulose, and hemicellulose, inaccessible to reaction. This is further complicated since the wood pulp consists of cells with various sizes and chemical composition. This means that derivatisation of the wood pulp is difficult and results in inhomogeneous substituted cellulose derivatives. An increased accessibility is a critical prerequisite for a homogeneous or designed substitution of cellulose material. In this project we develop methods to increase the accessibility of the wood pulp, both by means of carefully selecting the starting cellulose material and increase its reactivity and accessibility. Different methods, i.e. mechanical, chemical, and/or enzymatic pretreatment, to increase the accessibility of cellulose materials to swelling and reactive agents at different hierarchical levels will be reported. A series of cellulose materials with different hierarchical structure will also be used for comparison.