Understanding “Curling” or “splaying” with Synthetic or Synth-blend Brushes:
Brush curling or splaying can be extremely frustrating. There are many factors in one’s process that can bring about such changes in your brushes—but ultimately it may be a property of the material itself that is at the core of the issue.
Common synthetic brush filaments are made of substances like Nylon, Polyester, or Polypropylene. These types of fibers feature some advantageous characteristics such as excellent bend recovery, chemical resistance, and high wet resistance.
However, I believe that the general curling issue is due to the uneven breakdown in the structure of the synthetic filaments themselves. The outer regions of the hair bundle filaments that are exposed to more aggravating factors do diminish faster—thus resulting in a sort of uneven “stress relaxation.” Hot water, solvents, and aggressive use (like scrubbing or stumbling), may significantly exacerbate these issues.
Additionally, brush hairs/filaments can indeed expand when they are wet (both natural hair as well as for most polymer filaments). As the brush dries by evaporation, the outside of the outer hairs will dry first - and in drying, it will shrink. As a result, the brush tends to further curl and splay.
So yes, you can minimize synthetic deformation by reducing how aggressively such brushes are being used, minimizing or eliminating solvent exposure, avoiding hot water when washing*, and making sure brushes are not inundated with water when left to dry (esp. upright so that water can collect within the ferrule.)
But even so—those perfect points won’t last forever.
*While it is common to hear that hot water shouldn’t be used when washing brushes due to potential damage, one company–Rosemary Brush Co., actually recommends using exposure to boiling water to “pull” a deformed synthetic back into shape. They state, “For any synthetic brushes [loosing] their shape you can hold them in boiling water for 30 seconds, this should help pull them back into shape.” You can find this recommendation here: Brush Cleaning – A Brush Makers Top Tips. I haven’t tried this but I’d be curious to hear from anyone who has.