www.tentsmiths.com is a maker of many historical and classic tent designs. A first time shelter builder is apt to buy a cheap plastic or canvas painter's drop cloth. Canvas has a very real caveat aside from wieght. Cheaper canvas will show many specks and discolouration in the weave. This is dirt and will produce severe breathing discomfort from a combination of contaminants ranging from feces to pollens. Again we have the same pros and cons over synthetic vs natural fibers. Canvas is heavier but also more flame retardent. Another key to canvas use is never touch it directly in rain. You will create a passage in the fibers for water to drip through.Once sealed, properly pitched and maintained, canvas can be remarkably waterproof.