Most suits are made from worsted (smooth) wool, or heavier wool fabrics like flannel or tweed. In the summer, good tailoring is comprised of light and/or open-weave materials like linen, cotton, seersucker, and tropical or fresco wools.
These suits are often in light neutral tones or highly colorful, and are typically less structured, plus even fully unlined, at times.
But the best summer suits will always make you look like a million bucks, no matter the temperature.