The effect of penetrants, viz., moisture, aqueous alkali halide soluti
ons and some common organic solvents on the aromatic polyamides Kevlar
and Nomex has been analysed. The saturation moisture content in Kevla
r fibres is dependent primarily on sample characteristics. The dynamic
process of moisture uptake is, however, controlled by the relative hu
midity of the ambient atmosphere. In case of organic solvents, the ext
ent of retention by Kevlar depends on the molar volume as well as the
presence of specific functional groups in the former. In contrast with
Kevlar, Nomex sheets are found to be impervious to most of the penetr
ants.