Final answer:
The stratum lucidum is the layer of the epidermis that contains flattened keratinocytes filled with eleidin, a protein that helps prevent water loss.
Step-by-step explanation:
The keratinocytes within this layer are flattened and filled with the protein called eleidin: you're referring to the stratum lucidum, a smooth, translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer is only found in the thick skin of the palms, soles, and digits. The keratinocytes in the stratum lucidum are dead and densely packed with eleidin, which is a clear, protein-rich lipid derived from keratohyalin. Eleidin provides these cells with their transparent appearance and plays a crucial role in preventing water loss.