The ability of a fabric to repel water comes from one of three sources: its inherent properties, weave, and finish.
Wool, for example, is inherently water repellent; however a felted wool will clearly hold out water for far longer than an open gauze.
Finishes applied to fabric when it comes off the loom or printing machine may include fully water repellent finishes, more often the fabric is bonded with another to achieve the required criteria and these are primarily for clothing.
Water repellent yarns have come on in leaps and bounds. Fabrics for outside use – gardens, balconies, awnings, for yachts and pool sides – are becoming better and better, to feel and look just like indoor fabrics, that can be left outside in all or most weathers.