I have a long thick lined cotton trench-coat that used to be waterproof at one time (Navy surplus), but 30 years later it isn't anymore and just soaks through.
It poured down yesterday, so the kids put on their wellies and I put on mine, and we went for a long walk through the woods. I need to re-waterproof my raincoat (Imagine a belted dark navy blue raincoat that schoolkids used to wear in the 50s & 60s).
I've seen sprays for wax type waterproofing and also silicon type. I don't want to end up with a waxed cotton type thing as it's a nice raincoat, but I don't know enough about these things to choose the right spray.
I know you lot will know.