Which term describes the mechanism by which the stratum lucidum regulates water permeability?

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Water permeability in the epidermis is mainly controlled by the structural proteins that form the barrier in the keratinized layers. In the stratum lucidum, the cells are rich in keratin, with keratinization giving the layer a dense, protective quality that helps limit water loss from the skin. That makes keratin the best term to describe the mechanism by which this layer regulates water permeability. Granular cells are involved in keratinization and lipid processing but are not the direct barrier mechanism in this layer, corneocytes are the outermost cells primarily associated with the stratum corneum’s barrier, and “water passage control” isn’t a specific biological term. So the protein responsible for the barrier effect here is keratin.