Why does my kitten knead and lick at the comforter?

There's an area of my dad's bed comforter where the thin top layer of fabric is ripped open, and my kitten loves to go there, knead around it, and licks the strips of fabric for several minutes until it's pretty wet. His cute little muscles are very tense when he's doing this. Why would he like doing that so much? He doesn't lick anything else around the house for excessive amounts of time.