The effect of the amount and type of montmorillonite (MMT) on the supermolecular structure, porosity, and properties of polyimidoamide (PIA) fibres has been investigated. An increase in the quantity of nanoadditive incorporated into the fiber-forming polymer from 1 to 5% results in a decrease in the strength properties of fibers. The level of the sorption parameters of PIA nanocomposite fibers depends not only on the nanoadditive content, but also on the type of modifier used to change the MMT properties from hydrophilic to organophilic. It has been found that the exfoliation of MMT depends on the chemical structure of its modifier. The exfoliation takes place when MMT is modified with aminododecane acid. (c) 2007 Wiley Periodicals, Inc.