Two different perfluoropolyether-based fluids, namely the unfunctionalized GALDEN SV90 and the dihydroxy derivative FOMBLIN ZDOL 2000 were employed as liquid samples in a poly(dimethylsiloxane) (PDMS) microfluidic setup, fabricated by soft-lithography techniques. The results of our investigation were compared with the behaviour of the low viscosity and high-fragility polyurethane structural adhesive (NOA721), that is well known as an excellent material for the fabrication of sub-micrometer structures by soft-lithography techniques, and whose structural elastic properties inside restricted geometric systems have been recently investigated.