For example, there are hips of silvertip brushes, but from a post of Mark Watterson's father (CEO of Vulfix/Simpson) that a friend paste me, he stated some years ago in an old forum that:
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Silvertip hair is extremely difficult to come by. It is only available in very small quantities and it would be near on impossible to mass produce Shaving Brushes filled in genuine Silvertip as some claim.
I have a Simpson's Silvertip and it is incredible, nothing at all like the other 'Silvertip' hair on the market which is mostly just bleached and otherwise chemically treated - same deal with High Mountain White and so on.