Which product you can use is decided by the coating on your flysheet, and the maker of the tent and the maker of the treatment both publish instructions that govern. This page explains what the decision hinges on; the bottle and the tent label tell you the rest.
Establish that it is actually the fabric
Before treating anything, work out what is wet and why. Three different faults look similar from inside.
Condensation forms on the inside of the fly from the moisture you and the ground produce, and it drips or transfers where the inner touches the fly. It is not a leak and no coating will stop it.
Seam failure shows as a wet line along a stitched seam, and it means the factory seam tape has lifted or the sealant has aged. That is a seam job, not a fabric job.
Coating failure shows as water soaking into a panel rather than beading on it, often with a tacky or flaking feel on the inside face of an older polyurethane fly. Only this one is a reproofing question.
Silicone and polyurethane are two different worlds
This is the compatibility rule that catches most people, and it applies to sealants, repair tapes and reproofing treatments alike.
Silicone-coated fabrics — described as silnylon or silpoly — reject ordinary adhesive tapes and conventional coatings. They need silicone-specific products, and makers say so on the packaging.
Polyurethane-coated flysheets take conventional self-adhesive repair patches and the polyurethane treatments sold alongside them.
The two are not interchangeable in either direction. Silicone product on a PU fly and PU product on a silnylon fly both fail, usually in the rain and usually at the worst moment. Find the coating on the tent’s specification sheet or the label sewn into the fly before you buy anything.
Two different treatments, often confused
A flysheet has two properties that are separately maintained.
The coating on the inside face is what provides the hydrostatic head figure the maker publishes in millimetres. It is the actual barrier, it is applied in manufacture, and where it has degraded the remedy is a coating product matched to the chemistry.
The durable water repellent finish on the outside face is what makes water bead and roll off. It is not the barrier; it stops the outer fabric wetting out and going heavy. It wears with use and with dirt, and it is refreshed with a spray-on or wash-in repellent — again, matched to the fabric and applied per the instructions.
A fly that soaks through has usually lost the second before the first, and the two products are not the same purchase.
Seams are a separate job
Seam sealant is matched to the same coating question, and it is applied to the side the maker specifies — commonly the inside face on a PU fly. Old, lifting tape generally has to come off before new sealant goes on, and the tent needs to be pitched or laid out so the seam is flat and accessible.
Do it dry, do it clean, and give it the curing time the product states. A sealant handled before it has cured pulls away from the stitch line and you get to do it twice.
What the whole thing rests on
Pitch the tent to work on it, so the panel is under its normal tension. Clean the fabric first, because a treatment applied over grit and mould bonds to grit and mould. Follow the tent maker’s care instructions and the treatment maker’s directions where they overlap, and where they conflict, ask the tent maker.
And keep in mind that the two published waterproofing figures — hydrostatic head for the flysheet and for the groundsheet — describe different fabrics with different lives. The floor takes a knee on wet ground and is usually the higher figure of the two; it also usually fails from abrasion rather than from age, which is what a correctly sized footprint is for.
The manufacturer's own instructions come first, and this page does not stand in for them. Every weight, packed length, hydrostatic head, denier, micron rating, lumen figure and temperature on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A weight is reported as the maker counts it, and is never restated as another kind of weight, because the two are not the same figure.
What people ask before buying
How do I tell whether my flysheet is silicone or polyurethane coated?
The specification sheet or the label sewn into the fly usually says, often as silnylon, silpoly or PU. Where nothing is stated, the maker's customer service can tell you from the model. It matters because sealants and repair tapes are made for one chemistry or the other and do not cross over.
Is a leaking fly always a coating problem?
Often it is not. Water appearing inside is frequently condensation rather than ingress, and a wet patch at a seam usually means the seam tape has lifted rather than that the fabric has failed. Establish which before treating the whole flysheet.
Last reviewed 6 September 2026