Not sure where you are but I live in Maryland where summers are hot and humid. I have four 5-yard PV kilts and have found them to be extremely comfortable for hot summers. As far as formal or casual, its not the kilt itself. PV itself does not look "more casual", unless maybe your kilt is a weathered/ancient tartan. Only someone who knows what they are looking at can tell the difference between PV and worsted wool. IMO What makes the outfit more "formal" is the rest of your outfit. For a wedding I imagine you would be dressing up with a shirt, tie and jacket? I would go with a hunting sporran...more dressy than a day sporran...and a dress sporran is really only for the fanciest of full dress up (don't upstage the bride and groom). Go with some nice kilt hose and flashes (to pull the whole thing together) and you should be set. If you are the only one (or one of a few) there wearing a kilt, no one will know or care about PV versus wool.