i have one of peto's bags, its ok, it is actually thick tarpaulin type material, it is coated in wax.
he does various types, check his website out, they are ok, very basic, but well made, at least the one I have is, its slightly smaller than I expected, and on his site he seems to get a lot packed in it, but as a daysack its spot on.
I have a proper waxed cotton messenger bag and rucksack, I use the rucksack every week as I work away, I love it, but I only get my work gear and wash bag in it, its from a company called 'TRAKKE' up in Glasgow, a little expensive but I will say very high end workmanship and material, I had it as a pressie from SWMBO for my half century. I can vouch for the waterproofness if that's a word! very comfortable and quiet.
I'm not affiliated or work, know, befriend, been paid or any other association with either peto or trakke, just passing on my opinion of their products.
Adam