We do not have much need for true summer suits here in the Bay area. If we have two days a year of New York style heat, that is fortunately about all of it unless one leaves the City. And I could probably count the number of suit wearing men outside of the City on my fingers.
That aside, when I visit Mr. Thomas Mahon in Cumbria next week one of the topics will be another warmer weather suit, this one a double breasted in a light gray Finmeresco cloth from Smith's Woolens. Finmeresco is a high twist weave like the chalk stripe fresco from J&J Minnis in the photograph, where the visible weave means the cloth is more permeable to air and so wears cooler than any worsted no matter how lightweight. That weave, which gives the cloth a bit of a rustic air that some dislike, means it also resists wrinkling.
Now I have nothing against lightweight worsteds and I even own a couple, but the heart of a summer wardrobe should, in my opinion, be high twist cloth of this sort. The light gray commission will be my sixth, and on the seventh day I will wear worsted. Or linen, depending on the occasion.