Might be an obvious question, but what kind of clothing is 袖通してない服? Sleeved clothing?
Thus, it should be clothes one has never worn before. Google also gets you a number of pictures of brand new clothes with the price tags and whatnot still attached.
TL: Oumagadoki Doubutsuen (29/37) || *NEW* HUNGRY JOKER (latest update: case.12+13) • Meet the Man: Sterling Cooper Ad Agency