Here is a glimpse of my collection of gas masks, paintball face masks, and respirators. These are what I base my steampunk leather and resin creations on.
Pictured above is a No. 43 showing the straps, with the buckles attached to the mask surround and the straps made up of four pieces of leather, riveted (or sewn) together. My second gas mask was Pachydermos, which combined elements of No. 43 and the canisters of my first respirator, the Bad Air Transmutator. It kept the same straps as used in No. 43.
My third gas mask was part of the Sentinel ensemble, shown above. The straps were once again similar to the first two, with slight design modifications.