At higher bulk DS values, where CTA domains form, this restriction in swelling is most pronounced. There is also major increases in the CtA values, preventing penetration into the fibre network. In these cases, the formation of defined CTA domains, is likely acting as a 'glue' holding the fibre network together and preventing swelling. The impact on the wet strength is also observed here, with the CTA domains offering elasticity, although the contribution from reduced H-bonding between fibres reducing fibre adhesion cannot be discounted here. In both the high and low DS cases crystalline fibrillar aggregates are retained -low DS acetylation is restricted to fibril surfaces and the high DS acetylation shows clear separation of CTA and crystalline cellulose fibrillar aggregate domains.