Kilts are generally made of wool, and wool has a bad reputation. Or maybe a warm one. Wool is actually really breathable and a great year-round fabric, better than cotton. I suppose how it’s made (how tight the weave, etc) could be a factor, but look into it sometime. Wool has a lot going for it as a very versatile material. I knit and the coolest things for me to wear on hot summer days are things I’ve knit from 100% wool. Mainly tank tops with loose stitches, so yes there’s more airflow, but the structure of wool fiber itself is just really breathable and nice. Naturally wicks sweat so it dries quickly, doesn’t tend to retain sweat smells and can have anti microbial properties, so rarely needs washing. I’m a big fan of wool lol