Nik Wax is good too, though it's better for jackets and outerwear than it is for footwear. £5 a bottle from any outdoors shop or online and can be used on any material. I've used it on all my jackets that aren't fully waterproof. Works in a similar way to Crep Protect and Fabsil in that rainwater just beads off, but it's a totally different product, it's a micro wax solution suspended in water, rather than an aerosol moisture repellent.