I’ve done in 3 layers: (1) Exterior is PUL (breathable, waterproof; often used in cloth baby diapers). (2) 100% cotton (this image shows a tea towel but I found it was too heavy so have switched to 100% cotton heavy T-shirt). (3) Filter pocket. This image shows cotton T-shirt but I’ve gone to athletic wicking. Nose is shaped with a this Pellon to give more shape & provide breathing space. Nose bridge has plastic coated garden wire inside a twill tape pocket.

http://www.jennifermaker.com/face-mask-patterns-cricut