Cobijarse means 'to shelter' or 'to take cover'. It's a beautiful and somewhat poetic verb that you don't encounter in every song, making it stand out.
In "Piel De Seda," the lyric asks, "Y alguna vez has visto al sol cobijarse con las olas del mar?" (And have you ever seen the sun shelter with the waves of the sea?). This imagery personifies the sun, suggesting a tender, almost intimate interaction with the ocean, creating a vivid and memorable scene that enhances the song's romantic and dreamy atmosphere.
The whole song is one long look. He watches her at night in a black dress and heels so high "que hacen que camine tan lindo" [that they make her walk so lovely], then keeps cataloguing what he sees — her smile, her eyes like little pearls, and the moonlight landing on "su piel de seda" [her silk skin], which is the title and the line the chorus keeps coming back to.
Almost nothing happens. He takes her hand, he kisses her, he loses his place in her gaze: "no hay palabras que puedan explicarlo" [there are no words that can explain it]. Only at the end does he look away from her at all, out to the sun and the waves, before admitting what he has known the whole time — "Comienza este sueño y no pienso despertar" [this dream begins and I don't plan to wake up].