Making fabric waterproof is important in many circumstances. Whether it's your shoes or your boat cover, cotton, canvas or leather there are a number of different treatments for making sure that water doesn't affect fabric. It's equally important that you note the difference between waterproof (impermeable to water) and water resistant or water repellent--which means that water can still affect the fabric, but it will take much longer.
To make fabric waterproof you need to apply a treatment that completely shuts out water. There are natural treatments, such as waxes and oils like beeswax and soya bean oil, which have been used for many years. However there are also chemical treatments for waterproofing material, such as aerosol silicone sprays.
There are a number of different materials that people may want to make waterproof, but generally the fabrics will be outside for long periods of time, or they will be worn by a person who's out in the rain. Leather walking shoes or jackets are one example, and canvas boat covers or awnings are another. Before the invention of rubberised fabric, rain gear was made of materials that had been treated with oil or even tar to repel rain from the wearer's body.
Which waterproofing treatment is most appropriate depends mostly on which fabric you're trying to waterproof. Leathers react best to oils and waxes, because the leather already contains a number of natural oils. Cotton can bond with silicone, but acrylic fabric cannot. It's important that you always check which treatments are intended for use on which materials.
Certain treatments will take longer than others. For example, waterproofing a pair of leather boots may take half an hour to apply, and several hours to fully absorb and dry. On the other hand, spraying a silicone treatment over an outdoor cushion may only take a few minutes to apply and less than half an hour for it to set.
Many waterproofing treatments aren't permanent, especially if the item that's been waterproofed is going to be left out in the elements for long periods. Boat canvas covers should have their waterproofing treatment repeated every few years, for example.