What Is Silpoly? Ultralight Dog Jacket Fabric Explained

What silpoly actually is

Break the word apart and it tells you most of what you need. "Sil" is silicone. "Poly" is polyester. Silpoly is a polyester ripstop woven cloth that has been impregnated with liquid silicone, which soaks into the fibers and cures into a thin, flexible, water-sealing layer that is part of the fabric rather than a coating sitting on top of it.

The ripstop part matters as much as the silicone. Ripstop is a weave with a reinforcing grid of heavier threads laced through the base cloth at regular intervals. You can usually see it as a faint checkerboard when you hold the fabric to the light. That grid is a "firebreak" for tears. When a thin fabric snags on a branch or a rock, the grid stops a small nick from running into a long rip. For gear that lives on a moving trail partner brushing past scrub oak and granite, that containment is the difference between a scuff and a ruined layer.

Silicone impregnation does two jobs at once. It seals the weave against water and wind, and it adds tear strength by binding the threads so they resist sliding apart under load. That is why silicone-treated ripstops feel slick and a little papery, then turn out to be far stronger than their weight suggests. Backpackers have trusted silnylon and silpoly in tents and tarps for decades for exactly this reason, and the same logic carries over to an outer layer.

Silpoly is polyester ripstop sealed with silicone, engineered to shed weather and to stop small tears from spreading.

Silpoly vs silnylon: the water question

Most people meet these two fabrics as a choice, so it helps to line them up honestly. Silnylon is silicone-treated nylon. Silpoly is silicone-treated polyester. On a spec sheet they can look nearly identical. On a wet ridgeline they behave differently, and the difference comes down to how each fiber relates to water.

Nylon is hygroscopic. The fiber itself absorbs a meaningful amount of water and swells as it does. Two things follow. The fabric gains weight in sustained rain, and it stretches, which is why a silnylon tarp goes slack and saggy overnight in a storm and often needs a mid-night re-tension. Polyester barely absorbs water at all. A silpoly shell in the same storm stays closer to its dry weight and holds its cut, so a hood or a hem that fit at the trailhead still fits three hours into the weather.

Polyester has a second advantage that shows up over a season rather than a single night: UV stability. Sunlight degrades nylon faster than polyester, and above treeline the sun is not filtered by canopy. A layer that spends its life in high, open, exposed terrain is soaking up more UV than one that stays in the trees. Polyester ages more gracefully under that exposure.

Nylon is not without its case. Fiber for fiber, it carries a slight edge in raw tear and abrasion strength, which is why some ultralight builders still reach for silnylon when their single priority is toughness at the absolute lowest weight. For a shell whose job is repeated exposure to wind, sustained precipitation, and high-altitude sun, the lower water uptake, the lack of sag, and the UV resilience of polyester win the trade. That is the reasoning behind our choice, and if you want the longer version of how we weigh trade-offs, our design philosophy lays it out.

Polyester takes on less water, sags less when soaked, and holds up better under sun, which is why we build the shell from silpoly rather than silnylon.

Why recycled silpoly on the Traverse Shell

All of the above is why the Traverse Shell is built from a recycled silpoly ripstop. It is the top layer in our system, the one that takes the wind and the precipitation so the layers underneath can do their quieter work. A protection layer has one primary job, which is to manage weather without adding meaningful weight, and silpoly is the fabric that lets it hold both ends of that at once.

The recycled part is a deliberate choice, not a sticker. The polyester in the shell is recycled content, and it sits inside our commitment to at least 50% recycled fabric across the line. We are careful about how we say that, because recycled content is one honest lever and not a clean conscience. If you want to understand what the claim does and does not mean, we wrote about recycled fabrics in dog gear in plain terms. For the standards that back these claims up, the Textile Exchange Global Recycled Standard is the reference worth knowing.

Made-to-order production is the other half of that story. We are not cutting a warehouse of shells that may never sell. Each one is sewn in Colorado when it is ordered, which keeps waste down at the source instead of after the fact. Small-batch, women-owned, and built the way we would want our own gear built.

A shell earns its place when the weather it stops far outweighs the weight it adds, and recycled silpoly is how the Traverse Shell holds that balance.

If you are choosing an outer layer, start with how we think about choosing an outer layer and learn how the layers stack. Silicone impregnation is one way to manage water; the other common finish, DWR, works differently and gets its own explainer in what DWR is and how to renew it. Before you compare gear pages on numbers alone, read our guide to how to read a dog jacket spec sheet. You can see how the shell fits into the full system across the Traverse series.

Adventure On.