Click on photo to enlargeThis is what acrylic does to brushes, I don't know why. It might be that the acrylic causes the bristles to become brittle so they break more easily. Such wearing-down doesn't happen with oils. For this reason I use cheap brushes for acrylics and replace them often. Just today I got four flats, sizes 7 to 9, for less than one US dollar each.
There are times, though, when the job needs a good brush, and for those times I have the set shown below, which I think are made of nylon or something similar. They have lovely spring and precision and are a joy to work with. They were far from cheap so I'm taking the very greatest care of them.
