At the very back of the Crispaire book, there used to be maybe four heavier fabrics. They aren't available any longer. My local tailor has an old book and you can see where these were scissored out. I can't remember if they were 13 or 15 oz. Someone told me they were woven by Minnis.
yes, there were a few heavy pieces at the back, heavier than minnis'
it was a 3 or 4ply
an aquaintance had a suit made of it