In conclusion, we have showed that gas-phase reaction with acetate anhydride presents a unique opportunity for selective modification of cellulose I and II substrates. The regioselectivity was more controllable than the corresponding non-, acid-or base-catalysed liquid-phase systems, especially at higher temperatures. This is highly beneficial for controlled surface modification strategies but also for situations where supramolecular 3D morphology should be retained, as with many delicate shaped cellulose objects, e.g., aerogels. It is hoped that this publication will contribute the chemical and analytical know-how required to quickly expand the scope, and the scale, of application for a wide range of sustainable cellulosic materials with complex 3D networks and morphologies.