... got the better of my ignorance. So I did some reading and watched a few more YouTube videos on braided line. No reason at all that you couldn't use it for furling leaders. And a braided line furled leader would probably float just fine with application of an appropriate floatant.

I am still curious about what you are trying to accomplish. Regarding a tighter furl - how much reduction do you favor when you furl your leaders. Way back when, when there were a bunch of folks posting and participating on this BB, it seems most talked about reducing 10%. How that became some kind of standard or norm is something that I never understood.

Personally, I have always gone for 20% reduction ( noting that I only use thread for my leaders, except a couple of nymphing leader made of fluoro which are much different in length and configuration than the thread leaders ). Greater reduction alone might account for the tighter furl that you are interested in. As to a heavy butt section, just add a few loops more for the butt section than you normally do. The combination of more loops on the butt section and 20% or more reduction might get you exactly where you want to be - or not.

If you want or need more strength and less stretch in a leader, braided line may be the way to go. But there may be alternatives to how you furl leaders ( either thread or mono ) that will produce leaders more suited to your purposes.