Arrrgh such a cool idea! A zip off cape, does it get any better than this? There are sooo many ways you could copy this, you could make your own waterproof one using using some cut out shower curtain (the cute ones they have at the pound store with pictures of rubber duckies on them would be good for festival wear!) or you could attached some jersey/wool fabric in this way to a grey marl sweater or cardigan. So many ideas! I can imagine how cosy it would be in winter if you made this using a load of thick soft wool fabric. I would even think about using buttons instead of a zip.
Image: Jak and Jil