One of these duly showed up on the doorstep. It is, as Temp asked earlier, Polartec 300, and is, as he added, good stuff. Very cozy. Heavier than the Rab Alpha Flash jackets, but possibly as breathable/wicking.
Quickly snipped off the silly blue zipper tags once I knew it was going to fit. Was worried about the sizing, but needn't have been. Patagonia sizes big, and L is fine for a borderline L/XL (6', 200lb, 45"chest). The XL would have been a bit swimmy..
In all, very mid-70s outdoor pursuits instructor, yet somehow lacking the bullying perv nuance