The part of the skin made up mostly of dead cells filled with keratin is the stratum corneum.

Here's a breakdown:

* Stratum corneum: This is the outermost layer of the epidermis, the skin's top layer.

* Dead cells: The cells in the stratum corneum have lost their nucleus and organelles and are essentially empty shells.

* Keratin: This tough, fibrous protein fills the cells, giving them strength and resilience. This is what makes the skin waterproof, resistant to abrasion, and able to protect us from the environment.

So, the stratum corneum acts as a protective barrier, thanks to the dead, keratin-filled cells.