The best kilt for me in a Maryland summer is my Sport Kilt. It's quite thin and made of a blend of polyester and something unknown, but you can machine wash it and the pleats stay where they are supposed to be (although it has sewn down pleats, which are an optional extra). I also have a Frugal Corner "13oz" kilt that is made of very thin acryllic and is almost as cool, but their customer service is not too good.

However, not all of my kilts are suitable for 90 degrees F combined with 90 percent humidity, which is what you have to deal with here. If I wear anything made of 16oz weight material, even if its only a 4 yd kilt, in these conditions it is too hot, period. Mind you, even then, jeans are worse than that, so it's all relative.