According to Obenauf’s:
Requests for a better water proofer to replace temporary and toxic aerosol sprays led to development of a safe, nontoxic, longer lasting spray for waterproofing non-leather and partial leather footwear such as hiking and hunting boots, work boots, gym shoes, etc. Water Shield’s higher silicon content lasts much longer than aerosol sprays. It also resists stains and enhances waterproofing on leather, but if used on leather it must be applied as an over coat to a preservative for complete and proper care of leather. As a surfactant it does not have the natural oils required to restore and preserve leather. Uses for Water Shield have grown and are still being discovered as it will virtually waterproof everything fabric, canvas, leather (even leather furniture), etc.