How to Tell If a Bag Is Truly Waterproof

You’ve probably seen bags described as waterproof, water-resistant, weatherproof or water-repellent. But what do those words actually mean when you’re standing in the rain with your gear inside?

The problem is that these terms don’t tell you the whole story. There isn’t one universal rule that defines exactly how much water a product must withstand before it can be called waterproof or water-resistant.

So instead of relying on the label, it helps to look at how the bag is actually made. The material, seams, closure and the conditions the bag is designed to handle all matter.

Here’s how to tell the difference and, more importantly, how to work out what level of water protection you actually need.

You’ll come across all of these terms when looking at bags and outdoor gear. Here’s what they usually mean in practice.

There is no universal official scale that defines exactly what water-repellent, water-resistant, weatherproof or waterproof must mean. The actual level of protection depends on the product, how it is built, what it is designed to handle, and how the manufacturer defines and tests it.

Let’s start with the big picture. A backpack is only as waterproof as its complete construction. The main material needs to keep water out, the seams need to stop water getting through, and the closure needs to seal the opening properly.

There’s also a fourth part that is easy to overlook: what the finished product is actually designed to handle. A bag made for rain does not automatically become an immersion bag just because its fabric and seams are waterproof.

That’s why it’s worth looking beyond the words waterproof and water-resistant and checking how the product is actually made.

The weakest point matters. A bag is only as waterproof as its complete construction. The material, seams, closure and overall design all need to work together to keep water out. Let’s look at each one, starting with the material.

Let’s start with the material, because if water can get through the fabric itself, nothing else can fix that.

So how do we measure how well a material keeps water out?

One common method is called hydrostatic head, or a water column test. In simple terms, water pressure is gradually increased against the material until water starts to get through. The result is given in millimetres (mm). The higher the number, the more water pressure the tested material can withstand.

You’ll often see figures such as 5,000 mm, 10,000 mm or 20,000 mm on waterproof-breathable outdoor clothing. These materials are designed to keep rain out while still allowing some moisture vapour to escape.

Waterproof bags and backpacks often use materials such as PVC or TPU. PVC and TPU are commonly used to make waterproof materials, which is why you’ll see them so often in dry bags and waterproof backpacks. Unlike waterproof-breathable fabrics used in outdoor clothing, they do not need to let moisture vapour pass through.

You may therefore see PVC or TPU used in waterproof bags without a hydrostatic-head rating. The PVC or TPU material itself provides a waterproof barrier, so manufacturers often do not specify a hydrostatic-head value in millimetres.

Even when the material itself keeps water out, the seams, closure and overall construction can still let water in. A material rating by itself can therefore give you an incomplete picture of how waterproof the finished bag actually is.

Even highly waterproof fabric becomes much less useful if water can get through the seams.

Traditional bag and backpack construction uses stitched seams. Stitching creates needle holes in the material, so those seams need some extra protection if the finished bag is meant to keep water out. Seam sealing and taping can reduce or close these potential entry points.

For waterproof bags made from materials such as PVC and TPU, high-frequency welding is especially useful because it joins the materials without creating needle holes. The materials are bonded directly, creating a continuous sealed joint.

Taped and glued seams can also provide good waterproof protection and are widely used in waterproof clothing and other products. How well they perform depends on the materials, tape or adhesive and how the seams are made.

DryTide waterproof bags use high-frequency welded seams. So if you have waterproof material and properly welded seams, two important parts of the waterproof construction are already covered. The next question is how the bag is closed.

This is where things get interesting, because even a waterproof bag still needs an opening somewhere. That opening is one of the parts you need to pay attention to.

Roll-top closures seal the opening by folding it over itself. How tightly you roll it, how many times you roll it and how you secure it all affect the result. For DryTide roll-top products, the guidance is to roll the opening tightly at least three times and secure it correctly.

Waterproof or airtight zippers work differently. When fully closed, the zipper creates a sealed opening without requiring you to roll the bag down. They give you quick access, although sealed zippers are generally tighter to operate than ordinary zippers.

A ziplock closure uses two interlocking plastic strips that press together to seal the opening. It is simple and can provide a very good seal when properly closed. However, it is less robust than some other closure types, and sealing the whole opening takes a little time. That is why ziplock closures are usually found on smaller products.

There is no closure that is automatically right for every situation. Think about how quickly you need access, how wide the opening needs to be and what kind of water exposure the product is designed to handle.

Now we can put the four pieces together. The material, seams and closure may all be highly waterproof, but the level of protection you get from the finished product still depends on what it was designed to handle.

A waterproof bag made for heavy rain can be excellent for cycling to work, hiking or travelling in wet weather. That does not automatically mean it is designed to stay underwater.

A product intended for boating, kayaking or other activities where accidental immersion is possible needs to be designed with that possibility in mind. The material, seams and closure all need to work together for that use.

The intended use can also affect how the finished product is tested. A bag designed specifically for immersion will be tested under immersion conditions. A bag designed for rain and splashes may not have been tested for prolonged underwater use because that is outside its intended use.

That does not necessarily mean another waterproof bag would fail during a brief accidental dunk. Many waterproof bags can handle this type of accidental exposure, but that does not mean they are designed or tested for prolonged immersion. If immersion is a normal part of your activity, look for a product with clear immersion guidance or a relevant rating.

In simple terms, the fourth element is the purpose of the product. The material, seams and closure should all be appropriate for that purpose and work together to provide the level of protection the product is designed to deliver.

A well-closed roll-top backpack made from waterproof PVC and constructed using high-frequency welding can float on the sea surface for an extended period of time when enough air is trapped inside. Floating, however, should not be treated as a flotation device or as proof that every waterproof bag is designed for prolonged underwater use.

You may also see an IP rating on some waterproof products. IP ratings are standardized under IEC 60529 and describe the water protection of the complete product or enclosure, rather than the performance of one particular material.

The useful part about an IP rating is that it comes with defined test requirements. Each water-protection level corresponds to specific test conditions. That makes an IP rating more specific than general terms such as water-resistant or waterproof, which do not have one universal set of requirements.

The water protection is shown by the second character in the IP rating. For example, the X in IPX7 means that no dust or solid-particle protection rating is specified, while the 7 identifies the defined level of protection against water.

Here are some commonly seen water-related ratings:

• IPX4 – Splashing Water: Protected against water splashing from any direction. This is suitable for exposure such as rain or splashes, but it is not an immersion rating.
• IPX5 – Water Jets: Protected against water projected in jets from any direction.
• IPX6 – Powerful Water Jets: Protected against stronger water jets than IPX5.
• IPX7 – Temporary Immersion: Protected against the effects of temporary immersion in water under the conditions defined by the standard.
• IPX8 – Continuous Immersion: Designed for continuous immersion under conditions specified by the manufacturer and the relevant test. The exact depth and duration need to be stated separately.

One important detail is that IPX7 and IPX8 are not simply better versions of IPX6. They test a different type of water exposure. A product designed to withstand immersion is not automatically protected against powerful water jets unless that protection is also specified or tested. Some products therefore carry combined ratings such as IPX6/IPX7.

Many waterproof bag manufacturers do not use IP ratings because IEC 60529 was developed for classifying the protection provided by enclosures, particularly for electrical equipment. Testing a soft bag to an IP rating is a specific process, and the result describes performance under that particular test rather than every type of water exposure the bag might encounter.

For a waterproof backpack, information about the material, welded seams, closure and real-world water protection can often give you a more useful picture of how the bag is designed to keep your gear dry.

It is also worth checking how an IP rating was established. If an IP rating matters to you, look for information about the test, the testing laboratory and the specific standard or test conditions used. A manufacturer’s own testing or declaration is not necessarily the same as an independently verified laboratory test.

A waterproof bag can provide excellent protection against heavy rain, splashes and spray without being designed for prolonged underwater use.

Waterproof does not automatically mean submersible. A general practical observation is that many waterproof roll-top bags can withstand a brief submersion, even when they are not specifically rated for it. However, this depends on the individual product, so always check the manufacturer’s product description.

This level of protection can be enough if you are worried about your bag accidentally falling into the sea or even floating on the water surface. But without an immersion rating or specific manufacturer guidance, a brief submersion should not be treated as a guarantee.

If you want to intentionally submerge the bag for more than just a moment, you should look for bags that are specifically rated for submersion. A roll-top should not automatically be treated as suitable for prolonged immersion unless the manufacturer specifically says it is.

Also, always check how the manufacturer says the bag should be closed. Even a highly waterproof bag needs to be closed correctly to provide the protection it was designed for.

If you want to know whether a bag is genuinely designed to keep water out, you don’t need to rely on the word waterproof alone. Check how it is made, how it is closed and what the manufacturer says it is designed to handle.

Here are some practical examples of water exposure. Use the table as a guide rather than a rating system. The same label can perform differently depending on the product, construction, closure and conditions.

Important: This is a practical guide, not an official waterproof rating system. Actual performance depends on the material, construction, closure and intended use of the specific product. For immersion-rated products, always check the specified depth and duration of the rating.