I've seen cotton poplin in various things -- from Brooks Brothers suits to Bill's Khakis. I assume in the case of suits, it makes for a lightweight summer casual suit. Is that correct? Also, in regards to Bill's Khakis: They come in either poplin or twill. Is poplin considered a shade dressier than twill, or is twill dressier? I would like to pick up a few pairs of Bill's Khakis to starch and crease them and wear them with some nice polos, short sleeved shirts and what not for a clean relaxed Friday kind of look. Any recomendations as to twill vs. poplin?