We present experimental and theoretical results onintrusion-extrusion cycles of water in hydrophobic mesoporousmaterials, characterized by independent cylindrical pores. Theintrusion, which takes place above the bulk saturation pressure,can be well described using a macroscopic capillary model. Oncethe material is saturated with water, extrusion takes place uponreduction of the externally applied pressure; Our results for theextrusion pressure can only be understood by assuming that thelimiting extrusion mechanism is the nucleation of a vapour bubbleinside the pores. A comparison of calculated and experimentalnucleation pressures shows that a proper inclusion of line tensioneffects is necessary to account for the observed values ofnucleation barriers. Negative line tensions of order $10^{-11}\mathrm{J.m}^{-1}$ are found for our system, in reasonableagreement with other experimental estimates of this quantity.