If you make your tent out of ordinary “canvas” you are going to get wet in the rain. Canvas is a stout cloth, probably named after cannabis (Latin: “hemp”), made by tightly weaving material, mostly cotton, wool, and linen. This definition has not been that precise forever since the word canvas has come to signify any type of durable simply woven natural fabrics. There are different forms of canvas. Those differences are seen mainly in the fabric used for weaving and the chemical used for added capabilities.
Simple canvas is woven so that string goes under, then over the next perpendicular string; it is the simplest and tightest possible weave. The simple weave not only means that canvas is cheap and easy to make, but that it dries quickly, which is important for a fabric that is often used and stored outdoors. Modern canvas painter’s drop cloths are typically made with simple canvas. It also does not hold its shape well making it unsuitable for most clothing. Sometimes linen is added to simple canvas to make it more durable. Linen is made from fibers of the flax plant and is harder to work with than cotton but stiffer and the finished product lasts longer. Due to the labor involved in deseeding cotton in the 18th Century, linen was also is significantly cheaper (the opposite is true today).
Duck is the heaviest grade of cotton canvas. It is typically made with twice as much fiber going in one direction as in the other direction. The advantage of duck canvas is that it holds it shape. Perhaps the most common and famous application of duck canvas was Levi Strauss’ durable pants for the Gold Rush miners in California.
The problem with all of these canvases, however, is that when they get wet, they hold the water. While it is possible to make oilcloth from simple canvas by painting it with linseed oil (pigmented or not) and make it temporarily waterproof those oils wash out of it very easily. So, if you really wanted something to keep you dry, you used wool which with its lanolin which obviously keeps the sheep from shrinking when they get wet.
A wool tent, however, would be WAY too heavy for any practical purpose. Which brings us to the town of Duffle in the Austrian Netherlands (now Belgium). Duffel is a thick coarse WAXED canvas made from a blend of cotton, flax and wool. It has both the properties of canvas being durable and light weight but is also water repellant.
In the early middle ages, sailors noticed their sails caught better wind when wet. But wet sails are heavy sails making them difficult to handle (especially in storms). Dutch seafarers and chandlers, however, soon determined discovered that they could apply oils and waxes to their sail fabric and get the same effect. Waxed sails would catch the wind but not soak up the water.
This practice spread quickly and soon all manner of waxed canvas was common in northern Europe. Linseed oil was blended with beeswax and then to sailcloth. This produced a lightweight water repellant and strong fabric. More importantly, because of the wax, the oil in the duffle canvas doesn’t easily wash away so the effect is permanent. Eventually sailors even made their capes and other clothing from this waterproof fabric. One downside to the linseed oil, however, was that it yellowed as it aged – which is why fisherman’s slickers are traditionally yellow.
After its initial creation and use at sea, waxed canvas spread to other military applications. Being waterproof, waxed canvas was the fabric of choice for military clothing and equipment. Armed forces used waxed canvas for uniforms, tents, and duffles because of its durability, comfort, and water resistance.