fashion, one may use partial pressures instead of concentrations. Types of absorption Absorption is a process that may be chemical (reactive) or physical (non-reactive). Chemical absorption Chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption. This type of absorption depends upon the stoichiometry of the reaction and the concentration of its reactants. They may be carried out in different units, with a wide spectrum of phase flow types and interactions. In most cases, RA is carried out in plate or packed columns. Physical absorption Water in a solid Hydrophilic solids, which include many solids of biological origin, can readily absorb water. Polar interactions between water and the molecules of the solid favor partition of the water into the solid, which can allow significant absorption of water vapor even in relatively low humidity. Moisture regain A fiber (or other hydrophilic material) that has been exposed to the atmosphere will usually contain some water even if it feels dry. The water can be driven off by heating in an oven, leading to a measurable decrease in weight, which will gradually be regained if the fiber is returned to a 'normal' atmosphere. This effect is crucial in the textile industry – where the proportion of a material's weight made up by water is called the moisture regain. See also Lamm-Honigmann process References Physical chemistry Gases Gas technologies