Brush cleaning is the cheapest performance upgrade in this hobby, because a well-kept mid-priced brush outperforms a neglected expensive one every time. The mechanism is simple: paint that reaches the metal ferrule dries there, wedges the hairs apart and never comes out. Everything in a brush care routine exists to stop that happening or to delay the point at which it has.
What washing actually removes
Rinsing in water removes the paint you can see. What it does not remove is the film that works its way up towards the ferrule during a session and the pigment that settles into the base of the bundle. Brush soap is a conditioning cleaner that lifts that residue and leaves the hairs slightly dressed, which is why brushes washed with it feel and behave differently after a few sessions. Working the brush gently into the soap, rinsing, and repeating until no colour comes out is the whole technique, and it takes under a minute.
What brush restorer can and cannot do
Brush restorer is a stronger cleaner intended to soften and lift dried paint from a brush that has been neglected. On a brush with a modest amount of dried acrylic near the base it often works, and a splayed point can sometimes be coaxed back with restorer, careful reshaping and drying under a little tension. What it cannot do is undo hairs that have been permanently bent or forced apart by a solid plug of dried paint in the ferrule. That brush is finished, and buying restorer in the hope of rescuing it is money better spent on a replacement.
The habits that matter more than the products
Three things preserve brushes more than any cleaner: never loading paint past the belly, rinsing before the paint on the brush starts to tighten, and reshaping the point and storing it tip-up to dry. A painter who does those three consistently will get long service out of inexpensive brushes. A painter who does none of them will destroy expensive ones, and no product on the shelf changes that arithmetic. The soap is worth owning; the habits are what it is protecting.
Questions people ask about brush soap
What is brush soap for?
Lifting the paint residue that plain water leaves behind, particularly near the ferrule, and conditioning the hairs. It is the single most useful thing to own alongside a good brush.
Does brush restorer really work?
On moderately neglected brushes, often. On hairs permanently splayed by dried paint wedged in the ferrule, no. That damage is not reversible.
How should I dry a brush?
Reshape the point with your fingers or your lips, then stand it tip-up in open air until fully dry. Drying bristle-down or sealed in a case is what spoils brushes and ferrules.