Cycle rain cape, Water proof, but open underneath .. so therein lies the ventilation..

Mine is PVC , nylon reinforced .. Grundens, made in Portugal
A Fishing Offshore foul weather gear maker.. $120 @ Riv Bike

I have a Showers Pass Portland jacket and a Burly One before that.

there is still dampness going into the 'breathable ' fabric.. pores..
and rain running into the Pit zips. even closed (Zipper Choice)

The jacket is OK , long enough to unlock the bike when it's parked in the rain.
then I Pull the Cape On over it..