The Canadian C4 gas mask is the current issue respirator of the Canadian armed forces, but is being slowly replaced by the C5. The Defense Research Establishment of Ottawa (DREO), production started in the early 1980s and the mask serves as an excellent example of the "Fourth Generation Respirator".
The mask 
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The mask was originally black, but adhesive issues were subsequently discovered, and to clearly differentiate current issue masks from the faulty version, the amended masks are green or tan.
The Canadian C4 has convex dual polycarbonate eyepieces that provide a reasonable field of vision, in contrast to masks with circular flat lenses.
The profile of a more common green C4 gas mask. Note the drinking tube and the head strap.
The mask itself is made of butyl rubber. A voice diaphragm is located beneath the eyepieces, and more modern versions include drinking straws. The filter canisters can be attached on the right or left side, allowing both left and right handed users to sight weapons. Astride of the voice diaphragm is either an exhale valve or an inlet valve, depending on the model. The mask has a six-point fabric head harness, with only two adjustable straps, the adjustable being the bottom ones below the user's ears.
The C4 surpasses NATO and related Triptych requirements for face, eyes and respiratory tract protection against chemical and biological warfare agents when used with an approved filter/canister.
References Edit
Defence Research ESTABLISHMENT SUFFIELD RALSTON (ALBERTA), Assessment of Commercial Alternatives to the C4 Mask For Use in Moderate to High Risk Biological Scenarios
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