Otter Wax, waterproof your fabric:
Thanks to Frederic for bringing my attention to Otter Wax. Waxing natural fibres to make them waterproof is not a total new invention, more a forgotten practise. Probably the only company who still does it until now on a large scale is Barbour. But actually you can waterproof your shoes, backpack, jeans or jacket with a bar of Otter Wax quite easily.

Available is Otter Wax via their webshop in the US and in Europe via Warenmagazijn.