The Neptune Series 4750 is Princeton's synthetic version of a squirrel brush that might actually outperform the natural hair brush. Princeton describes Neptune as their "softest and thirstiest synthetic brush" able to deliver a ton of color, evenly. These brushes are more durable and affordable than real squirrel too! Neptune brushes are great for watercolor.
The Princeton Neptune Professional Series Set contains: Aquarelle 3/4", Round 4, Round 12, and Oval Wash 1/2".