In this work, we focus on percolating carbon nanotubes (CNT) networks deposited by inkjet printing on ethylene tetrafluoroethylene (EFTE) substrates. It was demonstrated that such devices constitute highly reproducible flexible strain sensors, whose resistance grows linearly with a gage factor close to 1 up to 600 µµ [1]. In the prospect of developing a physically-based model describing the resistance variation of these sensors under strain, the local motion mechanisms arising at the CNT network scale need to be understood. To this end, a setup was developed in order to observe CNT networks deposited on ETFE substrates submitted to tensile strains inside a scanning electron microscope (SEM). SEM images of CNT networks are thus obtained at different strain levels and processed by digital image correlation. This gives access to the strain fields developing at the scale of CNT networks and highlights local motion mechanisms arising within such networks when strained.