Forget crinkly linen or southern-gent seersucker. The coolest summer suits are made of seven-ounce, 190-gauge tropical wool. “Cotton and linen sound lighter,” explains James Jurney of Seize sur Vingt, “but the truth is, they don’t breathe.” Light to the point of transparency, tropical wool is just strong enough to be stitched without tearing. (In fact, it’s too thin for some—Dunhill’s master tailor, Bruno Cosentino, can do seven ounces, but prefers to work with eight. “It holds its shape better,” he explains.)
Once you’ve nailed down the lightest wool, there are other tricks to staying cool while looking smart. Never go for double-breasted in the summer, and have your jacket partially lined in the sleeves but only a third of the way down the back, stopping just below the shoulder blades. It’s an expensive way to make a suit, Jurney explains, because it’s very tricky to hide seams. But a good tailor can do it, and will for a price (approximately $2,000 at Seize sur Vingt)—which, as anyone who’s sweated through a suit while racing to a meeting knows, is well worth paying.