Isaqua, Imitation Sable brush by Isabey. Ultra-precise, lively, and springy. Made for more detailed work. Isaqua is a synthetic fiber brush which has the properties close to the sable-hair one. This hair, which has both responsiveness and springiness, will enable you to carry out high-precision work. It comes in four shapes: Fan, Round, Round Long Pointed Rigger, Flat Long Pointed Rigger.
Isaqua 6241i Round Brush Size 4 Watercolor Brush – Isabey.