Water-Repellent vs Waterproof: Which Do You Need?

What Is the Difference in One Sentence?

A repellent finish makes water bead and run off the surface, and a resistant construction stops water getting through it when something pushes. The first is a surface property of a cloth. The second is a property of a construction, and no finish alone delivers it.

What Does a Spray Rating Describe?

How the face of a cloth looks after water has been sprayed at it under stated conditions, rated against a standard scale. It is a surface behaviour, it is quick, and it is the right requirement for a product that will meet rain in passing. It tells you nothing about what happens when a loaded bag is set down in a puddle.

What Does a Hydrostatic Result Describe?

The height of a water column the material held before it passed water through, under a stated method. It is a pressure behaviour, and it is the right requirement where the product will be set down on wet ground or carried against a wet back. The figure is meaningful only with the method beside it, since the procedures differ in how they load the specimen.

Where Does a Bag Actually Let Water In?

At the seams, at the closures and at the base, in that order in most cases, and through the cloth last of all. A stitch line is a row of holes, a closure is a gap with a lip, and a base is the part that sits in whatever is on the ground. A requirement that describes only the cloth addresses the route water uses least.

What Does a Coating Do and Not Do?

It stops water crossing the face, and it does that well. It does not close a stitch hole, it does not seal a closure, and its own durability is a separate question from the level it achieved when new. A coated cloth in an untreated seam is a construction with one good element and three open routes.

What Does a Laminate Do?

The same thing a coating does, more uniformly, and with a film that can be welded. The weld is the point: a laminate is what makes it possible to join two panels without a stitch line at all. Where the requirement is resistance rather than shedding, that is the reason to choose it over a coated cloth.

Why Do Seams Decide the Outcome?

Because the seam is the weakest part of every construction and the part most often left unspecified. A requirement stated for the cloth and not for the joint is a requirement that will be met on the swatch and missed on the bag. Name the treatment for every joint in the wetted volume, and the requirement becomes checkable.

What Role Do Closures Play?

A large one, because a closure that does not span the opening leaves a gap at each end and a lip along the top. A chain closure spanning the whole width, with a treated panel behind it, is the configuration that works. A flap held by a spot closure, whatever its quality, leaves the corners.

What About the Base and the Edges?

The base is where the load and the water meet, so it needs its own treatment and its own seam position, kept off the ground where the pattern allows. The edges are where a turned construction can carry water inward, so they need binding or to be built so they do not present an open edge to the water.

How Does the Requirement Differ by Use?

A bag carried in passing rain needs shedding and a treated base. A bag set down in it needs resistance and a welded seam. A bag holding ice needs the liner and the seams treated but very little else. Working out which of those three the product meets is the whole of the specification, and it costs less than specifying all of them.

What Does Ageing Do to Each?

A finish wears off, and a laminate does not wear off in the same way but it can delaminate. Both effects are slower than most buyers expect and faster than most suppliers say. The right evidence is a result after stated cycles, which converts a claim about durability into a figure that can be compared.

What Claims Can Be Made?

The ones the evidence supports, in the words the evidence supports. A spray rating supports a shedding statement, and a hydrostatic figure supports a resistance statement up to that figure. Neither supports an unqualified word on a product page, and an unqualified word is what a customer complains about when the bag gets wet inside.

How Is Each Evidenced?

A spray rating on the cloth for shedding, and a hydrostatic result for resistance, both to named methods, and then a result on the joint whichever of the two was specified. Three measurements at most, and the third is the one that predicts whether the bag keeps water out.

What Is the Most Common Mistake?

Specifying the cloth and leaving the construction. It happens because the cloth is what a data sheet describes and the construction is not. A requirement written as one adjective on the material produces a bag that meets the requirement and still lets water in.

• Name the behaviour, then the method, then the figure.
• Treat every joint in the wetted volume, not only the cloth.
• Span the opening with the closure rather than covering it.
• Give the base its own treatment and its own seam position.
• Evidence the joint, since it is what fails first.
• Evidence the finish after cycles rather than only when new.

How Is Each Verified on Arrival?

Draw at AQL 2.5 under ISO 2859-1 General Inspection Level II. Confirm the specified seam treatment is present on every joint, confirm the closure spans the opening, and retain a panel from the delivery so a spray rating can be taken later. Those checks take minutes.

What Records Help Next Season?

The behaviour, the method, the figure, the seam treatment for each joint and one retained panel. Five items, and the retained panel is the one that settles an argument, because it can be tested again a season later.

What Does a Finish Do to Breathability?

It reduces it, because a finish that stops water crossing one way also slows vapour crossing the other. Where a panel sits against a body or holds damp contents, that matters. There is no setting that stops liquid and passes vapour freely, so the requirement has to be a decision about which of the two matters more.

How Should the Liner Be Specified?

By what it has to do: carry abrasion, wipe clean, or stay dry. A wipeable liner is usually a film or a laminate, and either changes how the panel behaves at a seam. A liner that stays dry is a closed-cell material, and it belongs alongside the insulation rather than inside it.

What Does a Taped Seam Do That a Bound One Does Not?

A taped joint closes the stitch line directly, so the treatment is inside the seam where the holes are. A binding covers the stitch line from outside, which protects it but leaves the holes open underneath. Taping outperforms binding for resistance; binding is often enough for shedding.

How Is the Opening Treated?

By spanning it. The closure has to run the full width of the opening and sit on a treated panel, or the gap at each end undoes everything behind it. A flap over an opening is a shedding detail and not a resistance one, however heavy the fabric in it.

What Does the Requirement Mean for Making Up?

Welding and taping both add operations, both constrain which materials can be used, and both need skill that is not present on every line. A requirement written without regard for the operation produces a sample that passes and a production run that does not, because the operation was never specified.

How Does Abrasion Affect the Result?

It removes a finish progressively and it can polish a laminate until it behaves differently. Both are slower than a laboratory result implies and faster than most suppliers say. The evidence that matters is a result after stated abrasion cycles, taken on the treated construction.

What Does Soil Do to a Finish?

It defeats it. A soiled face wets out even when the finish is intact, because the soil holds the water against the surface. Where a product will be used hard, that is a stronger argument for a laminate than for a finish, since a film is not defeated in the same way.

How Should a Water Requirement Be Evidenced at Goods-In?

Confirm the specified seam treatment is present on every joint, confirm the closure spans the opening, and retain a panel from the delivery. Those three take minutes between them, and the retained panel is what makes a later test possible.

What Should the Approval Record Carry?

The behaviour, the method, the figure, the seam treatment for each joint, the closure arrangement and one retained panel. Six items, and the sixth is the one that lets the other five be re-checked.

• The behaviour named as shedding or resistance, not as an adjective.
• The method, and the figure required against it.
• The seam treatment, named for every joint in the wetted volume.
• The closure, named as spanning the full width of the opening.
• The base panel, treated separately from the walls.
• One retained panel from the delivered lot.

How Do the Two Behaviours Affect Warranty Wording?

A shedding requirement supports a statement about rain. A resistance requirement supports a statement about being set down in water, up to the figure evidenced. Neither supports an unqualified word, and an unqualified word in a warranty is a commitment the evidence does not match.

What Is the Right Order of Decisions?

Use first, behaviour second, method third, then the seam treatment and the closure last. Working in that order produces a requirement that can be evidenced. Working from the material list forwards produces one that usually cannot.

1. Decide whether the bag meets rain, sits in water, or holds something cold.
2. Name the behaviour that use requires, as shedding or as resistance.
3. Name the method and the figure that will evidence it.
4. Name the seam treatment for every joint in the wetted volume.
5. Name the closure arrangement, then evidence the finished article.

How Should a Requirement Be Set From the Use?

Work out whether the bag meets rain, sits in water, or holds something cold, then write the corresponding requirement with its method and its seam treatment. Products that need only shedding are often built for resistance, which costs more and handles worse. Products that need resistance are often built for shedding, which is where the complaints come from.

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