Rex brushes?

[Rob72]

Did a search and came up with one (not really helpful) hit.

I don't see info on them, so...

Are they skunk-hair? Nasty synthetic? Akin to using monkey-butt fur to make lather?

Or, are they underrated/cheap but serviceable, credible handles if re-knotted? Dated, but comparable to VDH, or...?

An inquiring mind would like to know. Thanks!