Thanks all! Those explanations are at least as good as those I could give. :)
On the neoprene, Eric - I'm kind of a material snob and Neoprene has a lot going for it. I couldn't find anything that could do all of what I wanted the sleeve to do as well as neoprene - insulate for lifting, protect the kettle, not slide off. Even though it's a bit heavy, the material has a lot of integral characteristics that make it an elegant solution.
I find both reflectix and fiberglass rather ugly. Both would also require some kind of adhesive to fix them to the kettle wall and I didn't want to do that. And fiberglass can splinter.
Since silicone is, loosely, a rubber rather than a foam, it's actually heavier per volume than neoprene.
Having said that, I do offer the bare kettle for those who want to experiment. The lightest and most multi-function option I've come up with is folding it up in a handkerchief in transport and then rolling the handkerchief up and looping it around the boiler to lift it. It takes some practice, but can be done. I'll probably need to provide an illustration of that technique at some point.
Edit: Sorry for misspelling your name Eric!