The term Smoothing brush can be defined as, or has a description of “Decorating tool. For smoothing out bubbles in freshly applied wallpaper.”
The Smoothing brush is a decorating tool that is used to smooth out bubbles in freshly applied wallpaper. The bristles are made from nylon or horse hair and help get rid of air bubbles.
One of the very few single use tools that a DIYer will need in his tool bag.