I believe, for shelter purposes, it undergoes a further waterproofing process, but of this I am not certain.
"Camp and Trail"
Stewart Edward White
After waterproofing the worn patches on them with candle grease, and sewing up the front of the neck, where a "soufflet" or extra piece was let in to enable one to enter the garment from the top, and binding the legs and arms with strips of cloth, we felt pretty certain that little or no water would enter during the short passage of the moat.
"The Escaping Club"
A. J. Evans
16mo, leather, 1 50 Mierzinski, S. waterproofing of Fabrics.
"Seasoning of Wood"
Joseph B. Wagner