Store bought foam brushes are an inexpensive alternative to bristle brushes for small areas and difficult to clean finishes such as 2 part epoxies and stain. Even though their not very expensive we still hate to waste a foam brush for a small touch-up job.
A great alternative is to use a piece of self-adhesive foam insulation as the brush. The foam can be stuck to a scrap piece of wood or the handle of a used foam brush.