"Sil-Nylon", or siliconized nylon

What is "siliconized nylon"? Siliconized nylon, or "sil-nylon", is normal nylon that has been impregnated with silicone during the manufacturing process. Most tents on the market are made with a polyurethane coated fabric. This makes for several significant differences in the two fabrics, with sil-nylon being a superior fabric for use in a tent application.

Polyurethane coated fabric has coating on only one side of the fabric (usually the inner side), which means that any rain or condensation will soak into the exposed fibers on the uncoated, exterior side. This makes drying a long process, as that water can only dry out of those fibers as fast as it can evaporate from the fabric surface. Since it usually rains only on cloudy days :), the sun won't be helping that drying process, and as a result you get to carry a water-sodden tent on your back all day, or at least until you can stop hiking for as long as it takes for you to get the tent to dry out. Remember - water weighs a bit more than 8 lbs per gallon, so one cup of water weighs a little over 1/2 pound, or 8 ounces. Wouldn't you rather *not* be carrying around last nights rainstorm? It's heavy!

Sil-nylon, on the other hand, has none of those exposed fibers for water to soak into. The silicone treatment completely permeates the fabric fibers and forms a skin on both sides of the fabric. It is easiest to think of sil-nylon as being a layer of silicone with nylon fibers embedded in it for strength. Silicone is the stuff that is used to seal aquariums, bathtubs and sinks, and other applications where water must not be allowed to leak through. With a tent constructed of sil-nylon, all the water stays on the surface, and a quick shake will get rid of almost all of it, and its associated weight. A few minutes in the wind or sunshine and sil-nylon will completely dry out. You'll be miles further down the trail than someone with a wet, soggy polyurethane fabric tent.

Polyurethane itself will also absorb water! Water acts as a slow solvent to polyurethane. Never pack up a wet polyurethane tent for very long, or it will stick to itself and become one big ball of uselessness.

Silicone is hydrophobic - by its nature it repels water, and water will not act as a solvent on it. Your packed-up wet tent may get moldy if you leave it long enough, but you will be able to shake it right out.

Polyurethane coated fabric also doesn't age well. It is not uncommon for the polyurethane to begin to peel off as the fabric ages.

The silicone in sil-nylon completely permeates the fabric fibers - it *can't* peel off.

Why should the sil-nylon cloth be cut with a "hot knife"? In a word - Quality. Cutting the fabric with a hot knife keeps the weight down and keeps the quality up. Using a hot knife to cut the fabric fuses (melts) the edges of the individual fabric fibers together while it is being cut. While this won't entirely eliminate fraying of the fabric edge (nothing works all the time, right?), it will nearly eliminate it. The drawback to it is that it takes more time with this method because only one piece can be cut at a time. Cutting more than one piece ("stack cutting" - because multiple layers of fabric are stacked on top of each other before being cut) cannot be done with a hot knife - it would fuse the multiple layers of fabric into one thick layer on the cut edge. Stack cutting is usually done with a rotary blade, like a circular saw blade, and it leaves every individual fiber un-bound to it's neighboring fibers. If your edges aren't fused together, they will fray, and sooner, not later, unless you use some type of multiple fold on the edges, or a "binding tape" to hide and protect the non-fused edges. Both multiple folds and binding tape are extra fabric (and extra weight), and in my opinion, a lower quality, higher output solution.