Every tent eventually needs re-waterproofing. The question is which method to use. Silicone-based treatments and polyurethane (PU) coatings are fundamentally different chemistries designed for different fabrics, and applying the wrong one wastes time and money -- or worse, damages your tent. Understanding what your tent is made of is the prerequisite to choosing the right treatment.
Know Your Tent Fabric First
Tent fabrics fall into three categories, and which one you have determines what treatment to use:
PU-coated nylon or polyester. This is the most common tent fabric in mainstream backpacking tents. The Big Agnes Copper Spur, MSR Hubba Hubba, NEMO Dagger, REI Half Dome, and virtually all car-camping tents use PU-coated fabric for the rainfly and floor. PU coating is applied to one side of the woven fabric (the underside of the fly, the inside of the floor). You can identify it by the shiny, slightly rubbery feel on the coated side. PU coatings are typically rated to 1,500mm to 3,000mm hydrostatic head.
Silicone-coated nylon (silnylon). Used in ultralight tents and tarps from brands like Hyperlite Mountain Gear (though HMG uses DCF, not silnylon), Six Moon Designs, Gossamer Gear, and older MSR tents. Silnylon is nylon fabric impregnated with silicone on both sides. It has a slippery, slick feel and is lighter than PU-coated fabric of equivalent strength. Silnylon does not have a shiny coated side -- the silicone penetrates the fabric. Typical waterproof ratings are 1,200mm to 2,000mm.
Silpoly (silicone-coated polyester). A newer alternative to silnylon, used by brands like Durston Gear (X-Mid), Six Moon Designs, and LiteAF. Silpoly stretches less when wet than silnylon (silnylon can sag significantly in rain, requiring tension adjustment). The waterproofing chemistry is silicone-based, identical to silnylon treatment requirements.
Silicone-Based Treatments
What they are: Silicone waterproofing treatments are silicone polymers dissolved in a volatile solvent (usually mineral spirits or naphtha). When applied to fabric, the solvent evaporates and leaves a thin layer of silicone bonded to the fibers. Popular products include Gear Aid Seam Grip SIL, McNett Sil-Net, and Atsko Silicone Water Guard.
What they work on: Silicone-treated fabrics only. This means silnylon, silpoly, and any tent that originally used silicone waterproofing. The reason is chemical: silicone bonds to silicone. If you apply silicone treatment to a PU-coated tent, it will not bond -- it will sit on the surface and peel off, or worse, the solvents in the silicone treatment will soften and damage the PU coating underneath.
What they do NOT work on: PU-coated fabrics. Do not use silicone spray or silicone seam sealer on a standard PU-coated tent.
Application method for re-waterproofing a silnylon tent or tarp:
- Clean the fabric thoroughly. Silicone treatments will not bond through dirt, body oils, or old loose silicone. Wash with warm water and a small amount of mild, fragrance-free soap. Rinse until all soap is gone. Let dry completely.
- Dilute clear silicone caulk (100% silicone, like GE Silicone II) with mineral spirits at a ratio of roughly 1:4 or 1:5 by volume. The exact ratio is less important than the consistency -- it should be thin enough to brush on like paint, but not so thin it drips through the fabric. Test on a scrap if possible.
- Brush or roll the mixture onto the fabric in a well-ventilated area. Mineral spirits fumes are harmful -- do this outdoors or in a garage with the door open, and wear a respirator with an organic vapor cartridge.
- Let dry for 24 hours. The mineral spirits evaporate, leaving a thin layer of silicone chemically bonded to the silicone already in the fabric.
- The result is a rejuvenated silicone coating that restores waterproofing and adds life to the fabric. A quart of this DIY mixture costs about 12 USD in materials and will treat a large tarp or two-person tent fly.
Atsko Silicone Water Guard comes in a spray can and is the easiest commercial product for silnylon retreat. Spray on, let dry. One can (10.5 oz, about 10 USD) treats a two-person tarp.
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Durability: A properly applied silicone treatment on silnylon lasts 2 to 3 years of regular use. The silicone chemically bonds with the existing silicone in the fabric, so it does not wash out the way surface coatings do.
PU-Based Treatments
What they are: Polyurethane-based waterproofing treatments, typically water-based dispersions of PU polymers. They dry to form a continuous waterproof film. Products include Gear Aid Tent Floor Sealant (formerly known as Seam Grip TF), Kenyon Seam Sealer, and Aquaseal FD.
What they work on: PU-coated fabrics. PU treatments bond to the existing PU coating on tent flies and floors. They also work on uncoated nylon or polyester if you are trying to add waterproofing where none existed before.
Application method for a leaking PU-coated tent floor:
- Clean the floor thoroughly and let it dry. Set up the tent inside-out if possible to access the floor easily.
- Gear Aid Tent Floor Sealant comes in a bottle with a foam brush built into the cap. Apply an even, thin coat to the entire floor surface. One 8 oz bottle (about 13 USD) covers roughly 50 square feet, enough for the floor of a two-person tent.
- For pinhole leaks only, spot-treat the leaking areas rather than coating the entire floor. A thin dab applied to each pinhole is sufficient.
- Let cure for 24 hours at room temperature. The coating changes from white (wet) to clear (cured). Do not pack the tent until fully cured -- uncured PU will bond the fabric to itself permanently.
- For seam sealing on PU-coated tents, use Gear Aid Seam Grip WP (the regular formula, not SIL). Apply a thin bead along the inside of seams where factory tape has lifted. Cure for 24 hours.
Durability: A PU floor coating applied per instructions lasts 2 to 3 seasons. It eventually wears off from abrasion (feet, sleeping pad movement) and needs reapplication. The coating adds about 1 to 2 oz per square foot of coverage -- noticeable on an ultralight tent.
Comparison Table
| Property | Silicone Treatment | PU Treatment |
|---|
| Fabric compatibility | Silnylon, silpoly only | PU-coated nylon/polyester, uncoated fabrics |
| Bonding mechanism | Chemical bond to existing silicone | Mechanical and chemical bond to PU |
| Application method | Spray, brush, or dip (diluted) | Brush or roll-on |
| Cure time | 24 hours (solvent evaporation) | 24 hours (polymer cross-linking) |
| Durability | 2 to 3 years | 2 to 3 seasons of heavy use |
| Weight added | Negligible | 1-2 oz per 50 sq ft |
| Cost to treat 2P tent | 10 to 15 USD | 13 to 20 USD |
| Color/clarity | Clear to slightly hazy | Clear when cured |
| Temperature for application | Above 10C | Above 15C (cures slowly in cold) |
| Solvent/VOC | High (mineral spirits) | Low (water-based) |
| Touch-up friendly | Yes (respray spots) | Yes (brush on spots) |
The Critical Compatibility Rule
The rule is simple: silicone on silicone, PU on PU. If you are unsure what your tent fabric is, do this test: put a drop of mineral spirits on an inconspicuous area of the fabric (inside a stuff sack pocket, or the corner of the floor inside the tent). If the drop soaks in and leaves a dark spot, the fabric is not silicone-coated -- it is PU-coated or uncoated. If the drop beads up and does not penetrate, you likely have silicone-coated fabric.
What About the Fly vs the Floor?
Many tents use different materials for the fly and floor. The MSR Hubba Hubba, for example, has a PU-coated fly and a PU-coated floor -- same treatment for both. But some tents have a silicone-coated fly and a PU-coated floor. Check each component separately. Do not assume they are the same.
When Neither Treatment Is Enough
If a tent floor has multiple failing areas or the PU coating is peeling in sheets (delamination), coating over it with more PU will not create a durable repair -- the new coating will peel off with the old coating underneath. In this case, either replace the tent or, as a field-expedient repair, use a footprint (groundsheet) under the tent. A sheet of Tyvek HomeWrap (available by the foot from outdoor retailers or building supply stores for about 2 USD per linear foot) makes an excellent, lightweight footprint that does not require any coating.
For tents with widespread fabric failure, consider that re-waterproofing treats the symptom (leaking) but not the underlying cause (fabric degradation). Nylon loses roughly 5% of its tensile strength per year from hydrolysis in humid conditions. A 10-year-old tent with widespread coating failure may also have compromised fabric strength. It might be time for a new tent.