WW2 M-1 Helmet Liner - IMP.
Here is an original WW2 M-1 helmet liner.
The liner is made by IMP and the OD-3 cotton suspension is held to the liner by green painted A-washers. The leather sweatband is present.
The exterior of the liner had been painted at some stage and the brim has been modified to allow the chinstraps more movement.
A good used WW2 example...