what would be used historicaly?

I dont know i just enjoying doing the things that where done before

i like using the old methods, in this case linseed oil because it is easier for me to procure it, and probably cheaper than modern alternatives.  also, i want to retain the flexibility and softness of the fabric.  does anyone know if something like silicone spray would be able to preserve the flexibilty of fabric while providing superior moisture protection?

Are you asking what kind of oil you can use to treat fabric, like a cloak?

Originally wool had lanolin oil and was a natural part of the fabric even after it was woven. It provided a degree of water repelency. Modern wools have  the oils all washed out. In our experience, we have not been able to treat wool with an oil to make it like a hand spun, warp-weighted loom woven cloak could have been. In other words, "putting the oil back in" has been unsuccessful.

Best bet is to use Scotchguard. It will need to be reapplied once in a while. The sun will break it down along with repeated wear.

For cotton? I dunno. The is duck canvas out there aleady treated, but kinda heavy and stiff.

   Wool will remain warm, even if it's soaking wet, so if that's your concern, dont worry about it. ( It will be quite heavy, though).
  Scotchguard is good for waterproofing wool, but there is a down side to it. If your using it as a blanket, you really don't want it totally waterproof. It has to "breathe." What happens is that as you sleep, you shed moisture. If your blanket is so waterproof, that it can't go anywhere, it stays where it is, and you get wet.
  Scotchguard can also be used on cotton, but for my money, I would go with Thompson's Water Seal. the stuff is great, and it comes in a spray on version. Just re-apply as needed. However, any waterproofer is flammable, so be careful.

I would use the Scotchguard the fabric will remain pliable.  Oils will eventually dry or not and will be stiff or sticky and heavy, plus theres the whole self igniting issues with the linseed oil on a rag.  The best thing you can do is buy an emergency blanket or two, its a whole lot cheaper than any thing else mentioned above.

Horrible but will save your life if needed.  What are you exactly looking for and what are you wanting it to do?