https://techcrunch.com/2018/06/20/review-waxed-canvas-bags-from-filson-ona-croots-and-more/

If you’re looking for a good jacket or bag, you have your choice of materials: leather, heavy nylon, waterproof synthetic weaves like Gore-Tex… but for my money (and not a little of it either) the king of them all is waxed canvas. Pliant yet protective, wind and water–resistant but breathable, handsome to start but grows a character of its own, waxed canvas strikes, for me, the perfect balance of attributes. I drape myself in it, and in the case of bags, drape it from myself.

The main caveat is that it is not is cheap — sure, you can get a bag for $30 or $40 on Amazon, but if you want something that will live for years and years and get better with age, you’re going to be spending quite a bit more than that.