Waterproofing a Camping Tarp: Silnylon, Silpoly, and DCF Care Guide

A camping tarp is the most minimalist shelter you can carry. An ultralight silnylon flat tarp from Borah Gear weighs 8 ounces; a Hammock Gear DCF tarp with doors weighs 6 ounces for full coverage. At those weights, every gram counts -- including the grams of water that a saturated fabric can absorb. A wet silnylon tarp can gain 25 to 30 percent of its dry weight from water absorption, an unacceptable penalty when you are counting ounces. Keeping your tarp properly waterproofed is a weight-savings strategy as much as a weather-protection strategy.

Understand Your Tarp Material

Three materials dominate the ultralight tarp market, and they require fundamentally different care:

Silnylon (silicone-impregnated nylon): The most common tarp material for decades. Brands like Borah Gear, Etowah Outfitters, and older models from Mountain Laurel Designs use silnylon. It is a woven nylon fabric saturated with liquid silicone on both sides. When new, it is highly waterproof. Over time, the silicone coating wears thin from abrasion and UV exposure, and the nylon fabric itself absorbs water through microscopic gaps.

Silnylon's well-known weakness is sagging when wet. Nylon absorbs water and stretches, so a taut pitch at 9 PM is sagging by 2 AM as humidity rises and condensation forms. This is a fabric property, not a waterproofing issue, though a well-re-treated tarp sags less because less water reaches the nylon fibers.

Silpoly (silicone-impregnated polyester): A newer material gaining market share. Used by Durston Gear (X-Mid tarp), Simply Light Designs, and Warbonnet Outdoors. Polyester absorbs far less water than nylon (approximately 0.4 percent water absorption by weight versus 4 percent for nylon), so silpoly does not sag when wet. The silicone coating is the same chemistry as silnylon, so the waterproofing maintenance is identical.

Dyneema Composite Fabric (DCF, formerly Cuben Fiber): The premium ultralight material. Used by Hyperlite Mountain Gear, Zpacks, and Hammock Gear. DCF is a laminate of ultra-high-molecular-weight polyethylene fiber sheets sandwiched between polyester film layers. The polyester film is inherently waterproof. DCF does not need re-waterproofing in the traditional sense -- the film is the waterproof barrier, and it does not degrade from water exposure. What does degrade DCF is abrasion, UV, and repeated folding/creasing at the same points (which creates pinholes in the film).

How to Tell If Your Tarp Needs Re-Treatment

For silnylon and silpoly:

• Spray water on the tarp from a spray bottle. If it beads and runs off, the silicone coating is intact. If it soaks in and darkens the fabric, it is time to re-treat.
• Look for areas where the fabric appears lighter in color or feels less slick -- these are zones where the silicone has worn thin, typically at ridgeline tie-outs, ground-level corners, and anywhere the fabric rubs against something.
• If your tarp leaks in rain rather than just misting (a fine spray through the fabric, not actual dripping), you have coating failure that needs addressing.

For DCF:

• Check for pinholes by holding the tarp up to bright light. Pinholes appear as bright dots.
• Check crease lines where the tarp is repeatedly folded. The polyester film can develop cracks along these lines.
• DCF does not wet out. Leaks in DCF are from physical damage (holes, tears, film cracks), not from coating failure.

Re-Waterproofing Silnylon and Silpoly Tarps

The process is the same for both materials because both use silicone as the waterproofing agent.

Option 1: Commercial silicone spray (easiest)

Atsko Silicone Water Guard (about 10 USD for a 10.5 oz aerosol can) is the best consumer product for retreating silicone-coated fabrics. One can treats a 9x9 foot tarp with one coat.

1. Set up the tarp pitched taut -- this gives you a flat working surface. Do this outdoors or in a well-ventilated garage. Silicone spray solvents are volatile and toxic if inhaled in concentration.
2. Clean the tarp first. Wipe down with a damp cloth. Let dry completely. If the tarp is visibly dirty, wash it in a bathtub with a small amount of mild soap, rinse thoroughly, and let dry.
3. Spray Atsko Silicone Water Guard evenly across the entire tarp surface from about 8 to 10 inches away. Work in sections. The spray goes on as a clear liquid and dries to a slightly hazy finish.
4. Let dry for 24 hours. The solvent must fully evaporate for the silicone to bond properly.
5. Test with water spray. Apply a second coat if beading is still poor in spots.

Option 2: DIY silicone/mineral spirits (cheapest, best results)

This is the method used by cottage gear makers and long-distance hikers. It costs about 8 USD in materials and produces results that last longer than spray.

1. Purchase a tube of 100% clear silicone caulk (GE Silicone II, about 6 USD) and a quart of mineral spirits (about 4 USD at any hardware store).
2. In a disposable container, mix 1 part silicone caulk with 4 to 5 parts mineral spirits. Stir thoroughly with a disposable stick. The silicone will dissolve into the mineral spirits over several minutes of stirring. The result is a thin, paint-like liquid.
3. Lay the tarp flat on a smooth surface. Apply the mixture with a foam brush or a paint roller, working it into the fabric. The mixture should wet the fabric visibly but not pool.
4. Let dry for 24 hours. The mineral spirits evaporate entirely, leaving new silicone bonded to the existing silicone in the fabric.
5. This treatment adds negligible weight (the gram weight of the silicone solids, which is perhaps 5 to 10 grams for a tarp) while fully restoring waterproofing to the entire fabric surface.

This DIY method is chemically identical to what the commercial sprays do, at a fraction of the cost per square foot. It is messier and requires handling mineral spirits safely, but for a large tarp or multiple tarps, it is the economical choice.

What not to use on silnylon/silpoly:

• PU-based sealers (Seam Grip WP, Aquaseal) do not bond to silicone.
• Wash-in DWR (Nikwax TX.Direct, Grangers Performance Repel) is not designed for silicone-coated fabrics and will not bond.
• Standard tent waterproofing sprays for PU-coated tents contain different chemistry and will not bond to silicone.

Re-Waterproofing and Repairing DCF Tarps

DCF does not need re-waterproofing. What it needs is pinhole repair and abrasion management.

Pinhole repair: DCF pinholes are repaired with DCF tape. Zpacks and Hyperlite Mountain Gear sell DCF repair tape (about 5 USD per strip). Cut a piece of tape slightly larger than the pinhole cluster, round the corners (sharp corners peel), and apply to both sides of the fabric if possible. Press firmly for 30 seconds. The tape's adhesive bonds to the polyester film surface. A properly applied DCF tape repair is permanent and waterproof.

Abrasion management: DCF's weakness is abrasion resistance. The polyester film layer is thin (0.08 to 0.18 mil depending on DCF weight) and can be worn through by repeated rubbing. On a DCF tarp, abrasion typically occurs at tie-out points and along the ridgeline. Prevent this by:

• Using DCF tape patches at tie-out reinforcement points before the film wears through
• Avoiding pitching configurations where the tarp rubs against branches, rock, or rough surfaces
• Not stuffing the tarp into a stuff sack (which creates creases) -- instead, roll it loosely

Tarp Seam Sealing

Seams are the most likely leak point on any tarp, even one with intact fabric waterproofing. Most cottage-made silnylon and silpoly tarps are not seam-sealed from the factory -- you must do it yourself.

For silnylon/silpoly seams: Use Gear Aid Seam Grip SIL (the "SIL" is critical -- regular Seam Grip does not bond to silicone). Apply a thin bead to the inside of every seam, spread it with the brush tip, and let cure for 24 hours. One 1 oz tube (about 10 USD) seals all seams on a two-person tarp.

For DCF seams: DCF tape is the standard seam seal. Most DCF tarps come with taped seams from the manufacturer. If a taped seam is peeling, clean the area with alcohol and apply a new strip of DCF tape over the old one.

When to Pitch the Tarp, So to Speak

Tarp retreating has a point of diminishing returns. If your silnylon tarp has multiple large areas where the coating is gone (not just thin, but absent), and the fabric underneath has visible wear or UV degradation (fading, thinning, easy to tear), re-waterproofing is not economical or safe. A new silnylon flat tarp costs 50 to 100 USD from Borah Gear or Etowah Outfitters. An afternoon spent retreating a 10-year-old tarp with widespread fabric degradation is an afternoon you could have spent under a new tarp that actually keeps you dry.

UV is the primary killer of tarp fabrics. Nylon and polyester both degrade from UV exposure. A silnylon tarp pitched for 60 sunny days has measurably lower tear strength than a tarp used only at night. If your tarp use pattern involves a lot of daytime sun exposure (desert camping, above-treeline alpine bivouacs), expect a shorter useful life and plan to replace the tarp every 3 to 5 years rather than expecting it to last a decade.

For nighttime-only use in forested environments, a silnylon tarp re-treated every 2 to 3 years can last 8 to 10 years of regular use. The silicone coating protects the nylon from UV, so maintaining that coating is also maintaining the structural integrity of the tarp itself.