A stitched seam is a line of holes through a waterproof fabric, and taping is the strip bonded over it to close them. It is a separate claim from the fabric rating, it is the difference between rated cloth and a waterproof shelter, and it is where most listings stop explaining.
Why a seam is the weak point
Waterproofness is a property of a coating, published as a hydrostatic head in millimetres and quoted separately for a flysheet and for a floor. A needle passing through that coating leaves a perforation, and a seam is several hundred of them in a straight line, usually running down the parts of a shelter that shed the most water.
So a fly can carry a high hydrostatic head and still let water in at the seams. The two facts are not in conflict; they describe different parts of the construction.
What taping is
A tape is a strip of film with a heat-activated adhesive, bonded over the stitched line on the inside face. Done properly it seals the perforations and adds a little stiffness along the seam.
Where a maker says fully taped, the tape follows every seam. Where it says critically taped or names particular seams, the tape covers the ones the maker judged to matter and leaves the rest, which is a real difference on a shelter that gets pitched in bad weather.
A welded seam takes another route entirely: the two faces are bonded to each other without stitching, so there are no holes to seal. It is common on dry bags, where welded or taped construction is one of the specifications worth reading, alongside the fabric, the coating and the closure.
Where else it appears
On a bivy bag the taping matters as much as the fabric, because the fabric is rarely the limiting factor — and the same page of the specification should tell you whether the zip is a waterproof one or an ordinary zip under a storm flap.
On a tent, look for taping on the fly and on the floor separately, since they are different fabrics with different figures. On a tarp, a catenary-cut canopy may have a stitched ridgeline that the maker expects the buyer to seal, and that expectation is normally stated in the instructions rather than in the marketing.
Taping does not last for ever
Tape is bonded to a coating, and both age. Old tape lifts, curls and comes away in strips, which is what people find when a shelter that lived in a loft for a decade goes back up. That failure is visible from inside, unlike almost every other waterproofing problem.
Field repairs follow the fabric rather than the tape. Silicone-coated fabrics — silnylon and silpoly — reject conventional self-adhesive repair tape and need a silicone-specific tape or sealant. Polyurethane-coated flysheets take the conventional patches. A tent repair kit states which coatings its tape is intended for, and the two are not interchangeable: silicone tape on a PU fly and PU tape on a silnylon fly both peel, usually in the rain.
Check this before ordering
Three lines on the specification, in this order: the hydrostatic head for the fly and for the floor, whether the seams are taped and how completely, and what the coating is, because that decides what you will be able to repair it with. A shelter that answers all three is a shelter you can compare against another one.
If the seams are not mentioned at all, that is information too. It is worth reading the instructions before assuming the tape is simply an unstated feature.
What people ask before buying
Is a welded seam better than a taped one?
They solve the same problem differently. Welding bonds two fabric faces without stitching, so there are no needle holes to seal; taping covers a stitched line with a bonded strip. Dry bags commonly use welded or taped seams, and both beat a plain stitched seam, because a needle hole is a hole.
Which sealant do I use on a silicone-coated fly?
A silicone-specific one. Silicone-coated fabrics reject conventional adhesive tape and sealant, while polyurethane-coated flysheets take the conventional products. Makers state which coating theirs is for, so read the fly label before buying anything.
Last reviewed 6 September 2026