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To counter the spate of shitty threads, let's focus on making a quality one. I'll start by instructing you on how to waterproof fabric.
This will work on all fabrics, but works best on natural fibers such as cotton or wool. It will also work on artificial fibers like polyester, but has the risk of not absorbing properly on things like a nylon tent that is supposed to be water resistant on its own.
You will need a spray can of silicone waterproofing spray, available at most outdoor and sporting goods stores, and a bar of Greenland wax, which is a special blend of bee's wax and paraffin wax. Silicone spray can also be used to increase the water resistance of leather or suede (be aware, it may make the leather darker, so test it on a small, out-of-the-way section before spraying the whole thing), but the wax absolutely should not be used on leather as it won't absorb and will just form a layer of wax on the outside.
