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It started here: http://straightrazorpalace.com/members/hnsb/29-closer-look-shaving-soap.html
After that I looked at several other soaps.
The blog post didn't generate much interest so I never...

I agree.
Cushion has to do with how small of bubbles the soap forms when lathered - the density of the lather for lack of a better term.
Oil on your skin is slick but has no cushion. Airier soaps...

I think backbone is still a useful term. I prefer brushes with a lot of backbone. I could say I prefer a short loft, but I'm not interested in the loft. Loft doesn't translate across materials.