Sigma Synthetic Sigmax Duo by Sigma. $34.00. The Synthetic Sigmax Duo contains two of our best-selling brushes with classic black matte handles. The brushes in this collection feature the exclusive Sigmax filament, which allows for flawless makeup application without absorption into the fibers. The F82 is soft, dense and round for seamless blending of mineral products onto the skin. The F84 is soft, dense and angled for easy buffing of blush or bronzer onto the skin.