Aquash is a refillable brush that can be filled with water to use with watercolour paints or can be filled with dye or dye based inks to be used similarly to a brush pen.
The bristles are a durable, flexible nylon so they won't fray and retian their tip.
The easy-to-squeeze barrel & valve system allows the user excellent control of the flow of water or fluid and prevents colour caught in the bristle from being sucked up into the barrel & discolouring the water / fluid.
The medium tip brush is the most popular.
This video shows you how to clean the Aquash Water Brush