Permeable gear with the M3-IXA1-IVA1 Diaphragm gas mask. Permeable gear was used as early as WW1 and remained standard into the 1950s. My specific setup uses the second pattern “special” HBT uniform
Kimtech™ M3 Certifed Sterile Pleat-Style Face Mask with ties 62494 - 23 cm width, 200 sterile face masks