The Italian Maschera Antigas R.S.38 was similar to the S.I.P. 1 and L.B/v.n., but was made of light brown rubber, and used straps instead of the helmet design.  This example was made by Spasciani in 1938.

Maschera Antigas = "Gas Mask"

R.S. = Riccardo Spasciani

Similar masks in my collection:  Italian S.I.P. 1, Italian L.B./v.n.