Originally Posted by
smacw
Semi-Formal, outdoors, during the day? If I have that right, I believe you will need a coat and tie above the waist as non-kilt wearers would be doing so in strollers, lounge suits, though some may turn up in blazers and slacks. Waistcoat or vest is required with a stroller but optional with a lounge suit or blazer. In a kilt you will want a day wear jacket + matching or odd (solid color) waistcoat, and FIH tie. Definitely not a tweed jacket, and while I would prefer to see a jacket in dark gray or blue with plain buttons, an Argyle with matching black or odd grey vest is probably OK as they are readily available if not to my taste. But just a high collared vest?
Then again if the hosts has some alternate definition or vision for semi formal, who am I to say?
And we welcome a new expert to the forum! 
Thirsty Viking lives in Texas, where "fall" is mostly a thing on the calender, rather than a distinct "season"! Unless you get lucky, the 'fall' weather might still be a little hot for ties and jackets etc... In my real world experience at weddings around here, outdoors or otherwise, you are pretty unlikely to see jackets or ties of any kind on the guests anyway.
Order of the Dandelion, The Houston Area Kilt Society, Bald Rabble in Kilts, Kilted Texas Rabble Rousers, The Flatcap Confederation, Kilted Playtron Group.
"If you’re going to talk the talk, you’ve got to walk the walk"
Bookmarks