State of the Art, custom formulated stiff "synthetic bristle", a unique blend of varying filament thicknesses incorporating Robert Simmons special tapering techniques. Titanium brushes are extremely durable and designed for high performance use with oil and all types of acrylic, especially heavy bodied acrylic. Special "interlocked" process retains its shape and affords precise stroke control. The resilience and spring of the best interlocked bristle brushes combinied with a fine point and sharp edge; that will not lose its strength when wet. Every Robert Simmons brush comes with a LIFETIME GUARANTEE of quality!