I have some Fiberology PA12+CF15 blend (link) from a long time ago and recently got around to using it. I am amazed to say the least! It prints easier than PETG, even without an enclosure. Only downside is that it is much more expensive per kg, although it is lower density so I don’t seem to be going through it as quickly as other filaments.
I recently purchased some PC Blend with CF from Prusa as well. I haven’t gotten to print it yet, but I’ve heard very good things about it, too.
What less common filaments do you fine folks like using?
It isn’t. Think if the densest polyurethane foam you’ve encountered and then double it. I can dent it with my fingernail (takes some pressure, but it leaves a mark). Not sure if you’re familiar with the old glassine Estes rocket tubes (thin, quality cardboard, about 0.3-0.4mm) - but for structural integrity/stiffness it’s about like that in a 0.6mm single wall tube if the same diameter.