Natural vs. Synthetic Fibers
Natural animal hair brushes and synthetic fiber brushes are not the same, at all. There is a difference in how the brushes feel when painting and how the bristles spring back to shape. There is a difference in how the paint flows in the brushes. The biggest difference between the sable brushes and the synthetic brushes may be in how the brushes hold water.
Sable brushes, especially the rounds, are created so that the brush holds water or paint in the belly or wide part of the tuft and releases that water slowly. This allows for control over the flow of the paint and makes for long, thorough brush strokes. Synthetic fiber brushes tend to drop the water quickly at the first touch of the brush on the paper. Synthetics are less reliable in lifting water. Thus the brushes handle a little differently than sable.
For a watercolor painter, the investment in paint brushes is considerable. An artist must carefully choose the right brush for the style and technique of painting. The size and sha[e of the brush as well as the materials should be considered. Ultimately, it’s individual’s preference and goals of painting that determine the ideal materials in a paint brush.
if it changes its shape it may be of poor quality or you are applying too much pressure but if its stained you just prob use it alot or the color you used is dark
how to properly clean paint brushes
http://painting.about.com/cs/paintin..._Brushcare.htm
When I buy new brushes I tend to actually open the pack in the store and try to get a feel for them maybe that will help you as well.