Substantially dry, colloid forming particulate cellulose crystallite aggregates capable of forming an aqueous colloidal dispersion are made by forming a stable aqueous colloidal dispersion of cellulose crystallite aggregates together with at least 0.5% by weight of the cellulose crystallite aggregates, of a barrier material capable of preventing re-aggregation of the cellulose crystallite aggregates on drying from a colloidal dispersion, and drying and recovering the barrier material treated cellulose crystallite aggregates from the stable dispersion.  The stable aqueous colloidal dispersion may be formed by mixing the cellulose crystallite aggregates with the barrier material and reducing the size of at least part of the aggregates to a colloidal size, e.g. by subjecting them to a high-speed cutting action in the presence of an aqueous liquid, or to a pressure of at least 703 kg./sq. cm.  The barrier material may be hydrophilic and is preferably oleaginous.  The amount of oleaginous barrier material used should not exceed that sufficient to impregnate and completely saturate or coat the cellulose crystallite aggregates. In an alternative method, the cellulose crystallite aggregates are at least partially reduced to colloidal size, a stable aqueous dispersion thereof formed and the aggregates in the dispersion are impregnated with the oleaginous barrier material.  Specified oleaginous barrier materials include vegetable oils, e.g. castor, coconut, corn, cotton seed, linseed, olive, peanut, soyabean and tung oils; animal and marine fats and shortenings, e.g. butter, butter fat, cream, lard, oleo oil, oleostearin, tallow, fish, fish liver, whale oil, and margarine and hydrogenated fats and plastic fats; flavour essential oils, e.g. cinnamon, ginger and peppermint oils; other edible lipid and oleaginous materials, e.g. salad and cooking oils, salad dressing, French dressing, mayonnaise, cheese, milk, eggs, egg yolk, chocolate and peanut butter.  Other classes of agents include refined mineral oils and waxes, animal and vegetable waxes and oily and waxy esters of acids and alcohols.  Specified hydrophilic oleaginous materials include sorbitan mono-oleate, sorbitan monolaurate, and polyoxyethylene derivatives thereof, and among hydrophobic oleaginous materials specified are hydrogenated vegetable oils, saturated animal fats, sorbitan monopalmitate and mono- and tri-stearates.  Polyols and ether and ester derivatives thereof may also be used per se, or in combination with other agents, especially hydrophobic materials.  Examples include polyoxyethylene glycols and polyoxypropylene glycols, and the mono- and di-esters thereof with saturated and unsaturated fatty acids, methoxypolyoxyethylene and polyoxypropylene glycols and their ester derivatives, polyoxyalkylene glycols and their ester and ether derivatives, in which the oxyalkylene group may comprise recurring oxyethylene and oxypropylene groups.  Fatty acid esters, especially mono- and di-esters, of glycol, glycerol, sorbitol, sorbitan and other substituted polyhydric alcohols with monocarboxylic aliphatic, saturated or unsaturated, straight or branched chain fatty acids having preferably 12-18 carbon atoms, e.g. glycerol monolaurate and dilaurate, glycerol mono-oleate and di-oleate, glycerol mono- and di-stearates, glycerol monopalmitate, glycerol monomyristate, propylene glycol monostearate, propylene glycol monopalmitate, propylene glycol monopalmitate, propylene glycol mono-oleate, and mixtures thereof, sorbitan monolaurate; polyxoyethylene sorbitan monoesters, including the laurate, palmitate, stearate, and oleate; polyoxyethlene derivatives of mannitol; alkyl, aryl, and alkyl aryl ethers of polyoxyethylene glycol; glycerol sorbitan laurate, and sodium salts of fatty alcohol sulphates, e.g. sodium lauryl sulphate. The barrier material may also be a modified cellulose, e.g. sodium carboxy methyl cellulose, sodium carboxyethyl cellulose, sodium hydroxymethyl cellulose, sodium hydroxyethyl cellulose, water soluble hydroxyethyl cellulose, water soluble methyl cellulose, and water soluble ethyl cellulose.  Water insoluble and/or organic solvent insoluble ether derivatives of the cellulose crystallite aggregates, e.g. the hydroxypropyl and sodium carboxymethyl derivatives, and their oxidation and ester derivatives, including those of Specification 976,335, may be used, e.g. the carboxyl and aldehyde derivatives, and the phosphate, sulphate, acetate, and propionate. Other classes of barrier agents include protective colloids, especially natural gums, e.g. gum acacia, arabic, ghatti, guar, karaya and tragacanth; seaweed colloids, e.g. agar, carrageen, alginate, and alginate derivatives; seed extracts, e.g. locust bean, quince and guar, amylopectin; carbohydrates, e.g. sucrose, glucose, and other mono- and di-saccharides, starches, starch derivatives and converted starches, pectins, e.g. apple and citrus pectins and modified pectins, e.g. low methoxypectins.  Proteins and protein-containing source materials may also be used especially those having film-forming properties, e.g. milk casein, non-casein proteins, sodium caseinate, lactalbumin, lactoglobulin and the proteose-peptone fraction of skimmed milk, gluten, gelatin, soya protein, partially degraded soya proteins, egg white, egg yolk and albumen.  Other satisfactory amino compounds include amino acids, aliphatic and aromatic amines, e.g. lysine, triethanolamine, and morpholine. Mono- and di-esters of sucrose and fatty acids of, preferably, at least 12 carbon atoms, e.g. sucrose monolaurate, sucrose monostearate, sucrose mono-oleate, sucrose dilaurate, sucrose dimyristate, sucrose, distearate, and sucrose dioleate.  The proportion of barrier material used may be from 0.5%-70%, and in the case of oleaginous materials, is preferably 25-50%, based on the cellulose crystallite aggregates, which may be in the "never-dried" or "air-dried" state.  About 2%, based on the weight of oleaginous material, of an emulsifying agent, e.g. a polyoxyethylene derivative of sorbitol containing an average of 30 ethylene oxide units per mol may also be present. Specifications 874,945 and 976,335 are referred to.