notasheep,
I don’t have access to the book at this time but if I remember correctly (I read the book many years ago) the only source was discussing garments so thin such that they are see through. In such a case the Gemara in Berachos (25b) applies: ????? ?????? ???? ????? ??? ?????.
While many nylon stockings are see through and would be problematic, this should not apply to pants.