I designed this caddis fly to have a bubble back as an emerger. I use Bug Bond on the top of the thorax cover to produce this effect.
Notice the bubble back effect of the tinsel and the Bug Bond.
Hook: scud #14-16
Thread: 8/0 Uni brown
Rib: small copper
Body: marabou fibers dubbed on waxed thread, ribbed and brushed out to create fuzzy body
Wings/Legs: partridge feather "V" cut and folded back for thorax cover
Thorax: caribou underfur or hares ear dubbing
Thorax Cover: thin strip of holographic tinsel pulled forward over thorax cover... then apply a drop of bug bond on top and UV treat to harden.
Variations include: bead head, opal tinsel ribbing then used in the thorax cover, tan body and pheasant feather for wing and legs with squirrel dubbing for thorax. This fly is very effective as a dropper here on my home waters in NY in size #16 and size #14 in MT.