I have a Old Spice brush that I replaced the old Boar knot with a 24mm overstuffed TGN Silvertip in 2008..

I am quite abusive to that brush, and the hot tap water I have has been tested at 145° F I use near every type of lathering with that brush and it is quite well used.. Honestly I just haven't had an issue... Other than the slight reddish tinge from the Iron in our well water it looks and feels like the day I built it