Why does my dog find my underwear the most supreme thing to chew on?

I have three dogs. One of them is really good and mellow and would never chew on anything. The other two, however chew and destroy everything in their paths. Out of all the things they have mutilated (my biology textbook, brushes, kleenex, slippers, etc) their favourite thing is my underwear. I don’t understand exactly why they would find underwear, of all things so appealing. Can anyone shed some light on this troublesome problem of mine?