These consist of a mohair surface mounted on a pad of foam, bonded to a variety of shapes of handle. They are often called pad brushes. They give a very even but thin coat of paint, and cause less spattering than a roller.
Use pads instead of a paint roller or brush for smooth and lightly textured surfaces. Do not use on rough-textured surfaces, because these can snag the mohair and damage the pads.
Be sure to thoroughly clean pad brushes in water immediately after use. Dried paint will quickly ruin them.