I am thinking about attempting to make a bandanna water proof. Has anyone else tried that? Was it a good idea?

The aim is to make it better as a head-covering in the rain. I suspect a non-treated one will immediately get sodden and be useless. It might also be better for sitting on or protecting other gear. Ideally it'd be capable of carrying water (if tied into a sack shape) but I suspect that's unrealistically ambitious.

I'm aware that some uses rely on the bandanna adsorbing water (or blood or whatever). However, the ones I have in mind are silk, and thin enough for me to carry more than one, so I'd always have an untreated one available too. There are many uses where water-proofing is irrelevant, but where a bandanna works better than a plastic sheet.

I've not yet found a good source of 22" silk bandannas. I have a 42" one which I've cut into 21" quarters, and some poor quality 19" ones, so I'll probably experiment on one of those first. My favourite size is 34", and that is the size I'd ideally like to be water proof.