I love my 30mm that I got from Whipped Dog, it's synthetic and it feels like lathering with a big fluffy cloud. I also have a 24mm synthetic that is great with hard soaps.
My first brushes were small around 22-24mm boar and they were ok too ... i guess it's more the knot density loft and material than the knot size.
My first brushes were small around 22-24mm boar and they were ok too ... i guess it's more the knot density loft and material than the knot size.