The aim of this work was to reveal the moisture absorption–desorption–resorption
characteristics of epoxy and epoxy-based nanocomposites filled with different multiwall
carbon nanotubes (MWCNTs) by investigating the reversibility of the moisture effect on their
thermomechanical properties. Two types of MWCNTs with average diameters of 9.5 and 140 nm
were used. For the neat epoxy and nanocomposite samples, the moisture absorption and resorption
tests were performed in atmospheres with 47%, 73%, and 91% relative humidity at room temperature.
Dynamic mechanical analysis was employed to evaluate the hygrothermal ageing effect for
unconditioned and environmentally “aged” samples. It was found that moisture sorption was
not fully reversible, and the extent of the irreversibility on thermomechanical properties was different
for the epoxy and the nanocomposite. The addition of both types of MWCNTs to the epoxy resin
reduced sorption characteristics for all sorption tests, improved the hygrothermal and reduced the
swelling rate after the moisture absorption–desorption.