Living in Tennessee, I also had my share of kilt wearing in hot summers. I alluded to this in a post earlier, but to my estimation it's not just the weight of the fabric that matters, but how dark the colors are also. The bottom line is that dark colors soak up more heat. That's why people in desert climates wear a lot of tan and white. So I don't often wear my darkest kilt in that heat unless I know I'll be moving around (creating ventilation) or in the shade a lot.