Catdad,

You will probably find that the built-in air conditioning makes the kilt much cooler to wear than cotton slacks, or even shorts. I find that a medium weight, 8-yard kilt is pretty good in most weather up to about 100 F.

I'm working on a 4 yard box pleat. This or a 6 yard PV like the USAK semi-traditional may be the ideal hot-weather kilts. Many folks find that wearing a kilt belt makes the waist area much warmer. Without a belt, a wool or PV kilt will "breathe" from bottom to top, and help cool you off.

As someone suggested, it's an individual thing. Listen to your body, and hydrate!