Often referred to simply as "sil". Nylon fabric impregnated with a silicon coating on each side. Fairly economical. Typically offered in a 30 denier (30D) fabric weight, with lighter options sometimes available. Often used in lightweight shelters, tarps, and backpacks due to its strength, light weight, and waterproofness. Non-breathable.

Silnylon has been a popular backpacking fabric for many years, and although silpoly (sil-polyester) has gained traction in recent years, silnylon's popularity has been for good reason.

Silnylon Performance in a Backpacking Scenario

While very strong, silnylon fabric can sometimes suffer slight leakage under heavy water pressure such as that from a heavy thunderstorm (misting) or from kneeling against the fabric as water lies underneath. This can be seen when used in a groundsheet application for example, which could exert a high level of pressure against a very small portion of the fabric if kneeling on soaked ground (high PSI exceeding the hydrostatic head). Look for silnylon with a higher hydrostatic head rating to help in this regard.

Silnylon can “sag” when wet, requiring one to re-adjust their tarp or shelter. This has caused a surge of silicone coated polyester (silpoly) to be used in recent years, which stretches less and is more UV resistant, but not as initially strong, abrasion resistant, or as puncture resistant as silnylon (the stretch of nylon can be a benefit for durability).

For backpacking applications silnylon offers a nice blend of strength, abrasion resistance, weight, waterproofness, and value when it comes to budget. For complete waterproofing silnylon seams will need to be seam-sealed with something like Seam Grip SIL as the fabric cannot be factory taped. Some manufacturers use a fabric that is PU (polyurethane) coated on one side to solve this issue of taping (for example the Sea to Summit UltraSil Dry Bags), although the PU coating reduces the strength of the fabric.

Editor’s Note: This Jargon installment originally appeared in Issue 3 of TrailGroove Magazine. You can read the original article here.