A package arrived from Cumbria the other day containing the suit Thomas Mahon fitted this past July, just in time for the end of the season.
Intended for our San Francisco "summers" where temperatures rarely reach 75f (24c), the suit is made from Smiths' 11 ounce/330 gram Finmeresco. Finmeresco is smoother than other high twist fabrics of my experience, but that comes with a price as it does not seem to circulate air quite as well. In practice that will not be an issue as most wear will occur on days that are sunny but not hot.
After this one time out, the suit will be going back to have its full lining replaced with one that better complements a garment meant for mild weather. That will put it back in circulation about the time that sunny days return to the Bay area.