The first patent on gas-phase modification of cellulose, using gaseous acetic anhydride (Ac2O), was already published at the beginning of the 20 th century . Similarly, regenerated cellulose fibres (rayon) have been impregnated with aqueous potassium acetate and acetylated up to an acetate content of 35 % (bulk DS of 2.4), using gaseous Ac2O . Many more modern reports concern both gas and liquid-phase acylation of cellulose and nanocelluloses, many for the purposes of improving phase compatibility and behaviour in composites or suspensions . While many patents and publications have been made concerning gas-phase acylation of wood and cellulose, there are limited studies concerning the regioselectivity of these surface acylations, in part due to the absence of suitable high-resolution analytics. Consequently, our aim in the present manuscript is to better understand the regioselectivity of gas-phase reactions, using the classical acetylation as a model reaction. Thereafter, we showcase that gas phase reaction between acetyl anhydride can be tethered to the C6-OH of both cellulose I and cellulose II architectures, without disrupting the supramolecular structures of cellulose as well as the network of nanocelluloses.