At the risk of repeating what others have said, very probably more cogently:
All things being equal, I think it is fair to state that:
- a loosely woven cloth will wear cooler than a tightly woven one.
- a cloth with a nap will wear warmer than a “dry” cloth (e.g., a flannel v. a worsted)
- a cloth with a “dry hand” will last longer than a soft cloth (a worsted v. a flannel).
To stay cool in summer: do not run, do not walk in the sun, do not take public transportation, do not carry heavy packages. A lighter colour feels cooler, but that may be my imagination.
I do not own a suit from cloth weighing less than 12/13 oz. (a mid-grey worsted from Smith Woollens, ref. 3901, in a fairly porous weave). I am not sure I could follow this “rule” if I lived in the US. All of my other suits are 13.oz. and up, many in the 16 oz. range and above.
I don’t think my current tailors (Meyer & “Mortimer/Jones Chalk & Dawson) ever "pushed” me towards heavier cloths. I naturally start looking through the heavier ranges first (Lesser, Dugdale, Smith Woollens, John G. Hardy or P & H for tweeds). Too bad the books seem thinner and thinner as the years go by.
Frog in Suit