If you purchase footwear in a store specializing in camping or the outdoors you will find that leather boots come in two varieties. Chrome-tanned and oil-tanned. Ask the clerk. Today in the United States 90% of the footwear is chrome-tanned. For oil-tanned leather the drill (to make them water-repellant) is to apply grease or oil liberally, rubbing it in at the juncture of sole and upper. This is called the "welt". When sealing the welt keep the preservative away from the sole edges, which are often glued in layers. The preservative tends to dissolve the glue. For chrome-tanned leather use silicone wax, sprayed, brushed, or rubbed in as a paste. Never use oil or grease on chrome-tanned leather. It fills the pores so they can't breathe. The image is that of an oil-tanned boot.