Filbert brush. This reference
will allow you to blend and feather colors to obtain extremely smooth
colour transitions. It is also extremely useful for working with decals
and decal solutions. An extremely versatile brush for lots of painting
and weathering applications in models and dioramas. 

The Synthetic Brush range is made of high-quality fibres that offers
great spring. They are solvent-resistant and can be used with any type
of paint, including acrylics, enamels, and oils. These heavy-duty
brushes are convenient and affordable, making them a great option for
all kinds of painting and weathering techniques and applications.