Regarding rigidity, I haven't experimented with glues, but I have tried different numbers of cardboard layers. The one shown in the picture has three layers, and it's a little too stiff. The first one I made was only two layers, and I like it a lot better.

So far, all the tubes I've used came from rolls of Ultra Quilted Northern. But I've also wondered how other kinds of cardboard would work. Kleenex boxes come to mind. I like the curvature of a tube, though, because it makes the final product a bit more interesting.

Incidentally, I made the dumbwraps last week, and so far they're both working fine.

[Dr. Vector has spoken]