I like to tie a collar of cdc just like you would tie a hen hackle for a soft hackle - it is a really mobile soft hackle. However, I usually do it with a heavier fly - like a bead head nymph or soft hackle. One of my favorite caddis pupa flies was a body of glass beads, a dubbing thorax, and a turn of cdc like hackle. It worked pretty well for me. CDC is great for small flies since you can just break the fibers off to adjust length and it will look OK.