NOVELTY - Capsule, preferably a nanocapsule, microcapsule or macrocapsule, comprises a shell and a core. The core contains compound being at least at any temperature of not greater than 0-80 degrees C at 101325 kPa a liquid. The shell comprises semicrystalline cellulose nanofibers and/or semicrystalline cellulose nanocrystals having each a crystallinity index measured by X-ray diffraction of at least 30%.    USE - The capsule is useful for protecting a target compound against any selected from gases, radicals, chemical compounds and physical evaporation, preferably against any selected from ozone, oxygen, prooxidants, radicals and peroxides and more preferably against oxygen, where the target compound is preferably selected from fats, oils, colloids, micelles, food ingredients, drugs, dyes and arbitrary combinations of two or more of the compounds. It can also be used in a film, in a powder, in a foam, in a fiber, in an organic light-emitting device, in a solar cell, in an ink, in a thermal sensor, in an oxygen sensor, in a coating materials, in foodstuff, in a pharmaceutical composition or in a flexible display (all claimed).    ADVANTAGE - The capsule has an improved impermeability against gases, radicals, chemical compounds and particularly against molecular oxygen as well as an excellent mechanical stability, thus it can efficiently protect liquid enclosed in it, such as a food, a food ingredient or a photoactive composition, such as in particular a phosphorescent or triplet-triplet annihilation upconversion system (TTA-UC) composition, in particular against molecular oxygen for an increased period of time, which can be used in ambient atmosphere.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for preparing a capsule, preferably a nanocapsule, microcapsule or a macrocapsule, which involves: (a) providing a polar phase containing semicrystalline cellulose nanofibers and/or cellulose nanocrystals having each a crystallinity index of at least 30%; (b) providing a second phase containing: (i) solvent and/or dispersion agent being immiscible with the polar phase obtained in step (a), (ii) compound selected from monomers, oligomers, polymers and its arbitrary combinations and optionally: (iii) target compound to be encapsulate; (c) dispersing the second phase obtained in step (b) in the polar phase obtained in step (a); and (d) incubating the dispersion obtained in step (c).