I characterize this as a Korean War Era optical gas mask only because that is what was on a hand written tag in the box that this came in. I don't know if it is or not. Only other thing I can say about it is that it appears to me that it has never been used due to the string it is tied up with and the cardboard stiffener within the mask itself.
It is clean as a pin and it does say Army Lightweight Optical mask on the outside of the bag. The item "Korean War Era Army Lightweight Optical Gas Mask" is in sale since Sunday, February 7, 2021. This item is in the category "Collectibles\Militaria\Surplus\Personal, Field Gear\Gas Masks".
The seller is "mineralwa" and is located in Mineral, Washington. This item can be shipped to United States.