<p>The use of lignocellulosic materials as internal curing agents, attributed to their remarkable water-uptake capacity, is gaining attention as a cost-effective and sustainable solution. Milkweed fibres, distinguished by their exceptionally wide lumen, exhibit excellent hygroscopic characteristics, positioning them as ideal candidates for serving as internal curing agents. This study examined the coupled effects of fibre composition and lumen infiltration on the internal curing performance of Milkweed (MW) fibres, and their impact on pore network development in low water-to-cement (w/c) ratio cement pastes. Three types of MW fibres including non-treated (N), hydrothermally treated (HT), and hybrid treated (HY) were evaluated for differences in chemical composition and lumen accessibility. Nuclear Magnetic Resonance (NMR) relaxometry and Low-Temperature Differential Scanning Calorimetry (LT-DSC) were used to monitor water transport kinetics and pore percolation, respectively. Results show that fibres retaining lignin (N and HT) exhibited greater resistance to hydrate infiltration and slower water release, leading to a more disconnected pore structure. In contrast, HY-MW fibres, with reduced lignin content and increased lumen exposure, showed faster water depletion and higher capillary connectivity due to hydrate intrusion into the lumen. These findings emphasize the interdependent roles of fibre chemistry and lumen morphology in governing both the efficiency of internal curing and the evolution of the microstructure in hydrating cement pastes.</p>