Most painters have favorite brushes and distinct brush preferences. Some of these preferences may be purely sentimental. I have a Grumbacher “Gainsborough” size 16 China bristle that I bought over forty year ago. I treat it well and enjoy using it. I am also not very fond of synthetic bristle, probably just because it is synthetic and unnatural. But there is another, quite objective, reason behind brush preferences. There is a very real relationship between paints and the brushes used to apply them. Natural hair and natural bristle brushes behave very differently from synthetic fibre brushes. Oil paints and acrylic paints also behave very differently. Nobody who has tried out different brushes and different paints would argue about this. It is probably also the case that natural fibre brushes work best with oils and synthetic fibre brushes work best with acrylics. Paint made with natural media—oil and resin—wants (or at least deserves) natural brushes. And paint made with synthetic media begs for synthetic brushes.
Synthetic brushes have a somewhat different feel from natural brushes—they lack the snap of a hog bristle brush and the soft synthetics flex differently from sable and ox hair. My personal preference is for the natural bristle or hair brushes when painting in oil. Natural bristle responds beautifully to oil and resin. And properly cleaned after use, a natural bristle brush can last for decades, like my favorite Grumbacher, The issue with acrylics is very different. Given the use of water as a thinner and a cleaner in acrylic painting, a good natural bristle brush will have its characteristic snap at the beginning of a painting session but will gradually become more and more soft, even mushy, as painting progresses and water affects the bristles. A synthetic bristle will be impervious to the water and will retain its feel throughout the session. It is a good idea not to use the same brushes for oils and acrylics, given that cleaning procedures are different for oils and acrylics and that there is often some paint residue left in the bristles up close to the ferrule even if they are well cleaned. If you paint in both oil and acrylic, have two distinct sets of brushes, regardless of whether you choose to paint with only one kind of brush, natural or synthetic. I keep a full set of natural brushes with my oils and a full set of synthetic brushes with my acrylics. Any thoughts from others? What are your brush preferences?