Without knowing the originator of the Neversink Caddis here's a variation of the pattern. There are multiple variations with a segmented foam body, no foam head etc. but this is the pattern I've found fits best for my fishing and tying. The name 'Neversink' doesn't refer to its buoyancy but rather the Neversink River in New York. And some people will point out that this fly sink, and yes, all flies sink at one time or another but this fly floats extremely well.
Here's the recipe:
Hook: Ahrex Hooks FW 501/503
Body: 'Possum in olive
Wing/Body: 2mm closed cell foam
Wing: Nature's Spirit select cow elk
Hackle: Whiting Farms