Scotchgard was invented in the 1950s when a researcher with the 3M Corporation, who was assigned to develop a lining for jet fuel tanks, accidentally spilled some test material on a co-worker’s shoe. The stuff wouldn’t come off with the usual stain removers, and, eureka, an industry was born. Chemically, Scotchgard is a fluorochemical polymer, meaning it consists of a material that contains fluorine that is arranged to form large molecules from smaller units. What it does is form a barrier around the fibers of a fabric that is solvent resistant and moisture repellent by virtue of the fact that most liquids can’t cling to it. Dump something on it聴wine, coffee, whatever聴and most of it rolls right off.
Of course you can spray it on fleece. The stuff is harmless聴it’s all around us these days, in carpets and furniture聴and can be used perfectly safely on things you wear. Mind you, what it does is make a fleece jacket stain resistant. It won’t make it waterproof. Most outdoor garments already carry a Scotchgard-like material called a durable water repellent (DWR) coating. This helps water bead up and run off, although in time the water will overwhelm the DWR and saturate the garment surface. That will happen pretty quickly in a loosely woven garment such as a fleece jacket.
For what it’s worth, Nikwax makes a wash-in material聴 designed for fleece, wool, and similar materials聴that will enhance their water repellency. It’s called Nikwax TX-10 Polarproof, and sells for $11 a bottle. Just toss it and the jacket in the laundry, and wash away.