At an event this past weekend, I asked some men wearing kilts about the fibre content of their kilts and about their experiences of wearing wool in hot weather.
One man said that his kilt was acrylic. Another said his was wool, and he'd chosen to wear a kilt made from 10 ounce weight fabric as most suitable for the hot weather, and moreover, except for around the waist where the fabric is close to the body, the design of the kilt makes it comfortable in hot weather.
They had some tartan fabric on display and I got to feel the difference between 10 ounce fabric and a heavier weight which I believe from looking at the shop they recommended, Scottish Lion, could be as heavy as 16 ounces.
Another man, when he heard me asking about wool in hot weather, said that when he was young he wore a baseball uniform made out of wool. The team was told that wool would cause an evaporating effect with their perspiration and keep them cool, but he doesn't think it ever worked.