I use Rosemary Ivory and Classic Bristle and the Ivories do not splay in the washing process, but the Bristles would if I did not use my Cotton String technique! Firstly I will tell you I use Palmolive hand soap in a bar to wash them. It is soft and conditioning, for all brushes.
I always wash them gently, but not without thorough soaping and rinsing in cold/tepid at least twice rinsing in a deep flowing pot of water not pushing them on the bottom too much, but up in the water water sloshing vigorously.
If they seem discombobulated with my efforts to wash and rinse I use a cat wire brush to comb them straight on a flat surface. and then dry on a towel gently in the right direction.
The Ivory brushes just need to be gently stroked together and left to dry standing up in my holder.
The bristle brushes, after drying gently on the towel want to fluff at this point, so I stroke them as flat as I can and then take a short length of Cotton String, wind it not too tightly around the ferule and make a half reef knot gently in front then very carefully just slide the string over the ferrule onto the base and middle of the bristles. Left to dry upright they are great like this and ready to paint next session. See Photos…