Unfortunately, there’s no official regulation that dictates whether a 's backpack bag can call something “waterproof” or not. Yes, there are standards outlined by the IP system which shows exactly how waterproof or water-resistant something can be, but there’s no requirement for brands to use this in the creation of a product. Therefore, what’s waterproof to one organization might not be anything other than water-resistant to another. That being said, there are a few things you can look for that will tell you whether something is actually waterproof, water-resistant, or even completely submersible. These metrics are as follows:
IP Rating: Most obviously, if a piece of gear has been waterproof-tested to IP standards, brands will outline that clearly on their site or even on the piece of gear’s tags. The IP system can be fairly confusing, but if you understand how it works things are simpler to understand. At a glance, what you need to know is this: the higher the number, the more waterproof a piece of gear is. Something that has an IPX6 rating is splashproof, IPX7 can be submerged shortly(30 seconds). Something that is IPX8 can be fully submerged.
Exterior Materials: Without some kind of IP rating, it’s somewhat difficult to tell just at a glance what bags are waterproof and which aren’t. But if you see TPU or PVC laminates (or similar materials) in the exterior construction, there’s a pretty good chance that the fabric is at least impenetrable to moisture. It’s also helpful when brands, on their websites or on labels, mark that fabric is 100% waterproof. There are also some materials that are extremely water-resistant, but not impenetrable to moisture. Yes, it will likely keep out even the heaviest rainfall, but complete submersion will yield a different, soggier result.
Closures & Seals: Almost as important as the material itself, the seals and closures will determine true waterproofing. Something with stiched seals is inherently not waterproof, as moisture can slip between the seams. However, seams that are welded or taped are going to be far more water-tight. Similarly, there are both water-resistant and waterproof zippers — so keep an eye out for that. Lastly, many truly waterproof bags rely on hearty roll-top closures to create a waterproof seal. Not all of these closures are truly waterproof, but they can be extremely good at fending off impending moisture.
Submersion: The easiest way to see if something is truly waterproof or just extremely water resistant is to see if the brand themselves make claims as to whether it can be completely submerged. Bags that are submersible are a point of pride and will almost always be outlined as such. If a bag’s description doesn’t mention this factor, you’re better off assuming it can’t be submerged.