One "substitute" for CDC that I've written about before is poly yarn, and poly yarn is a favourite of mine, has been for many, many years and will continue to be so. It's strong, comes in umpteen number of colours, floats, holds floatant well and does well on the flies as wings, legs, shucks, thoraz covers etc.
There's a fly. Rackelhanan, by Swedish dry fly legend, Kenneth Boström, which is tied entirefly from poly yarn, and it's a magnificent fly as you can pull it under to let it pop up on the surface again, mimicking sedge behaviour as they oviposit.
Sometimes, though, poly yarn is a iittle to "clinical", too tidy, some would say, to look at. and usually when it's used on the simplest of flies. A dubbed abdomen, a wing and a dubbed thorax. That is in general a deadly emerger - just think of Bob Wyatt's legendary "Deer Hair Emerger". For that style of fly, I've finally started using a material that I first came in contact with many years ago - arctic hare's feet. A lovely material that's strong, fuzzy, very curly (ie. floats incredibly well) and is relatively easy to use.
And it's very durable, so the flies last app. forever (or until you bend a hook - or ding it, and you don't have your sharpener with you, Bernd :-).
It was T.Z.s flytying tutorials with artic hare's feet that got me back on track together with the flies Thomas gave me two years ago in Denmark. Several of them were tied with artic hare, and they did (and do) fish really well. I must say, I think it's here to stay this time. If you haven't, try them. If you can't get them at your local dealer, I think T.Z. can help you with some huge artic hare's feet in very high quality - ou know where to find him :-).
Have a great weekend!
PoD: Simple Artic Hare's Feet Emerger.