There are no good suitings for hot weather. Really. The English inventors of the suit did not face much heat over the course of their summer and accordingly did little to take it into account despite their experience in India. What we have available to us today are really suitings for the sea shore - cloths for 80 degree (27C) days with a breeze. When temperatures exceed 90F (32C) men can only sweat, or flee into an air conditioned environment.
Men considering warm weather suitings should begin by first throwing out a bit of the conventional wisdom. Dupioni silk is not a summer suiting. A ten ounce/300 gram tightly woven cloth, it wears warm and, like gabardine, is better suited to spring and early fall.
There are perhaps five cloth choices that do provide service on warm-but-not-hot summer days. Three of them are better choices for the workplace and the first is the most obvious: lightweight (7-8 ounce or 210-240 gram) tropical worsteds. These are light but not all that cool-wearing as their weaves do not allow much air ciculation. They also wrinkle too much for my taste but, nonetheless, they have their place. The best include H. Lesser's Tropicals and Smith Woolens' Gilt Twist.
The word twist leads us to a class of cloth that is to my mind the best hot weather choice. These are the high twist weaves that are woven to resist wrinkling and allow air circulation (this really works - I was wearing a pair of high twist trousers in a breeze the other day and had to look down to reassure myself that I still had them on). The slight downside to these is a moderately rough hand to the weave. Minnis fresco and Smith's Finmeresco are two excellent examples, with the Smith's considerably smoother to the touch.
The third choice are blends of mohair and wool, which are sometimes woven in a high twist weave as well. Mohair wicks away perspiration but gives cloth a bit of a sheen that can be offputting to some men. I prefer it for evening suits and dinner clothes. Harrison's Cape Kid, an 8 ounce/240 gram blend of 60% Summer Kid Mohair and 40% Super 100 wool, is a world class offering if a bit too lightweight for my taste.
Those three more formal cloths are joined by linen, which also wicks perspiration well but has a tendency to rumple, and cotton, which can be lightweight but creases easily. Either is effective for less formal occasions but leaves something to be desired in an office, though striped cotton seersucker and olive cotton poplin suits are American staples.
And those are the best of a poor lot when the weather is hot.