Sequential infiltration synthesis (SIS) is a vapor phase infiltration (VPI) technique to produce organic-inorganic hybrid materials and/or inorganic nanostructures through infiltration of an inorganic precursor into a suitable polymer template. SIS uses the same approach as atomic layer deposition (ALD) through introducing precursors/co-reactants in separate, sequential steps and exploiting self-limiting precursor reaction chemistry to deposit target materials. Despite the broad interest in and importance of SIS for semiconductor nanolithography, nanopatterning, organic electronics and water membrane technology, the number of inorganic materials that can be grown by SIS remains quite limited. To expand the library of materials that can be synthetized using this technique, widening its application fields and appeal, experimental and theoretical studies on the kinetics of sorption, diffusion and reaction mechanisms of precursors with the different polymer matrices are necessary. In this respect, the understanding of the fundamental physicochemical mechanisms governing the infiltration of SIS precursors and co-reactants into the polymer matrix is very important to help with developing modelling tools for SIS, similar to the state of modelling of ALD, with predictive capabilities, that will support the community in the search for novel precursors and the establishment of proper infiltration protocols.