Summer waterproof jacket that folds-up tiny?

Zippy

Expecting rain, I wore my Endura Venturi eVent jacket; whereupon the sun blazed and I did my boil-in-the-bag impersonation. (It wasn't that bad, really; the Venturi does 'breathe' well.) So I'm after a proper lightweight, small-folding waterproof, please.

Thanks, all.

Zip'.