I kept running across “Soap papers” it in my research about traveling. So I went down the rabbit hole. I also remember seeing paper soap dispensers in old buildings when I was a kid, in my memory they were sort of folded like rolling papers, so they wouldn’t stick together.
Turned out that the soap of my youth and the one they still make today, was just that all soap, but the soap invented in the 1880s was soap impregnated paper and was thus able to carry advertising.
Reithoffer & Neffe’s Soapsheets seem to have hit the market in 1882. Appealing to any man who wanted clean hands. . . adventurers and cyclists, it was heavily marketed to the medical field.
The only image I have been able to find is from 1893 Embalmers Supply Company catalog.
The clipping from 1894 Scientific American explains the process for making the paper.
The ‘soap case’ is from an embroidery kit from 1905 Butterick catalog. I added it for scale.