How to Waterproof a Hiking Backpack: The Complete Guide

How To Keep Backpack Dry

Imagine this: you’re midway through a two week trip in the Pacific Northwest and – no surprise – it starts to rain. A slow drizzle quickly turns into a heavy downpour, so much so that your rain jacket is just another layer of wet on your skin.

The rain continues for hours and, before you know it, you’re at camp, excited to put those dry clothes of yours on and get out of the rain. You open up your pack and all of your gear is soaked. Unfortunately, you forgot to waterproof your backpack. Looks like you’re in for a long, cold, uncomfortable night in your damp sleeping bag.

If this has happened to you before, we’re not surprised. In fact, this scenario is incredibly common among both experienced an novice hikers, alike. Thankfully, there’s a way to avoid this sad and potentially dangerous situation: waterproofing your backpack.

Waterproofing your backpack can help reduce your chances of rolling into camp after a rainstorm and finding that everything from your socks to your stove is soaking wet. However, there are many different ways to waterproof your hiking backpack, each with their own advantages and disadvantages.

Thus, instead of pretending like there’s a one-size-fits-all solution to pack waterproofing, we’ve created this complete guide to keeping your gear dry, regardless of the weather. Coming up, we’ll walk you through why you need to waterproof your backpack and the best ways to go about doing so. We’ll discuss the pros and cons of each method of pack waterproofing and even recommend the best use for each method. Let’s get to it!

Why do I need to waterproof my backpack?

If you’ve ever been caught in a situation like the one we described at the beginning of this guide, then you know firsthand why you need to waterproof your backpack. Simply put, wet gear is sad gear.

Although there are plenty of great new insulating materials out there that can keep you warm when wet, there is nothing sadder than putting a sopping wet synthetic puffy on top of your damp fleece and overly moist skin as you shiver in your tent that’s actively dripping water onto your head.

Beyond just being a sad state of affairs, however, being wet for a prolonged period of time is a surefire way to expose yourself to the dangerous and potentially life-threatening condition of hypothermia. To understand why this happens, we first need to discuss the four main ways in which we, as humans, can lose heat to our environment and get cold, known as the four types of heat transfer.

Evaporative Cooling

Our ability to sweat is actually one of our best adaptive mechanisms for surviving in a hot environment. When our core body temperature gets too high, our brain sends blood to our peripheries (our arms, legs, fingers, and toes) and to the surface of our skin so that we can draw water from our very warm blood, expose it to the surface of our skin and allow it to evaporate away. When moisture evaporates from our skin, there is a transfer of heat from our body to the environment, thus creating the cooling effect we feel from sweating.

Radiation

Radiation is the process of heat transfer through infrared energy waves, moving directly from the source of heat (such as a fire) to something else. Radiation is the reason why we like sitting by campfires at night – they pump out heat into the atmosphere, and if we’re close enough, we get to enjoy it, too!

Conduction

Conduction happens when we put two objects with different temperatures in direct contact with each other, like a person and the cold ground. Heat then flows from the warm human (core body temperature of 98.6°F or 37°C) to the cold ground (somewhere around 50°F-40°F or 10°C-4°C), which is why we get cold quickly when we lay on the ground. This is also why sleeping pads are an important insulating layer for us at night.

Convection

While evaporative cooling, radiation, and conduction are all important risk management things to consider when adventuring outdoors, the number one thing we need to consider when we’re soaking wet in the woods is the role of convection. Convection is the transfer of heat through liquids and gasses and it happens because hot air and liquids rise while cold air and liquids sink. This is the main reason why we have wind.

If you’ve ever been outside in a windy storm, you know that you get cold in the wind really quickly (something we like to talk about as the “wind chill factor”). Add onto that the effects of evaporative cooling and you’ve got a recipe for being really really cold when you’re wearing wet gear in a rainstorm, so cold that you could get hypothermic.

That’s why you should waterproof your backpack.

As an outdoor recreationist, it’s your job to keep your important gear, such as your sleeping bag and spare warm clothes, as dry as possible at all times. Sure, if you’re in the desert, you might not need to be too conscientious about this, but everyone else needs to take certain precautions to help ensure that their stuff will stay dry, regardless of the weather.

Foggy and raining conditions with hikers in a grassy meadow
A day where you definitely want to waterproof your pack in the Wind River Range, WY

What is the best way to waterproof my backpack?

Alright, now that we’re all on the same page about the need to waterproof our backpacks, it’s time to get into the nitty-gritty details about the different ways you can go about making your hiking pack storm proof. As we’ve mentioned, there are a number of different ways to make your backpack waterproof, each of which has its own pros and cons.

Thus, to help you make an educated decision about which method of pack waterproofing will work best for you in different situations, we’ll walk you through the each of the different methods and describe the advantages and disadvantages to each. Here we go!

 

Do nothing and hope for the best

Although this isn’t really a pack waterproofing method, per se, it’s important to highlight that not everyone chooses to do anything special to protect your gear from the rain. While this might sound like a ridiculous thing to do, if you live somewhere that gets very little precipitation (we’re looking at you folks over in the Desert Southwest), then it might not be worth the time, money, and effort to waterproof your pack.

Since the chance of rain is quite low in some parts of the world, when you travel in these places you can probably get away with this method of “waterproofing” your pack. That being said, as you can imagine, we don’t recommend this method pretty much anywhere except for particularly arid places.

Pros:

  • Involves no extra effort
  • Zero costs
  • Simple and easy

Cons:

  • Can go horribly wrong
  • Doesn’t waterproof your pack at all

Best Use: Day hikes and short backpacking trips in the desert and other arid environments.

 

Spray and Seam Sealer

The waterproofing spray and seam sealer method can be an effective way to beef up your pack’s built-in weather resistance for light rain events. However, this only really works if your pack is made from somewhat water-resistant materials as seam sealing and spraying a cotton drawstring bag or tote will do little for you in the long run.

To use this method, you’ll first want to go out and get yourself some waterproofing spray and some seam sealer. Then, you’ll want to make sure your backpack is as clean as it can possibly be. You can clean your backpack by spraying it down with a hose, then scrub it with a stiff-bristled brush. It also helps to submerge your backpack in a bathtub or bucket filled with warm, soapy water, before rinsing it off and hanging it up to dry.

After your pack is dry, you can spray it down with the waterproofing spray, following the manufacturer’s recommendations. Usually, you need to apply one or two coats of spray and then hang the bag to dry. Once the pack is dry, you can go through it and use the seam sealer to tape up all of the seams in the fabric. There are a lot of seams in a backpack, though so this might take you some time! Be sure to let the seam sealer dry compeltely before you use your pack.

This process isn’t the fastest, but it isn’t too labor intensive. In fact, much of this process involves waiting for your pack to dry, so there’s relatively little work for you to do. In the end, however, you end up with a pack that’s a bit more weather resistant than it was before, which can be helpful for combating light to moderate rains.

That being said, basically, “waterproofing spray” is what we call a “durable water repellent” or DWR. It does not transform your backpack into a fully waterproof pack. Rather, it helps encourage water droplets (i.e. rain) to bead up and drip off your pack instead of soaking through it. Seam sealer, on the other hand, merely prevents water from seeping through the seams of your pack’s fabric.

Thus, the waterproofing spray and seam sealer method, contrary to what the name might suggest, does not waterproof your pack, it just makes it a bit more weather resistant. Plus, you need to frequently re-spray and re-seam seal your pack, so it’s not a one-and-done thing. Therefore, we don’t recommend it as your only line of defense against the rain. Rather, it’s a great technique that can be used in conjunction with some of the other methods we’ll discuss shortly.

Pros:

  • Not very expensive
  • Increases your packs’ natural weather resistance
  • Requires no extra gear

Cons:

  • Doesn’t actually waterproof your pack
  • Packs require frequent spray and seam seal treatments
  • Somewhat time intensive

Best Use: As a second line of defense and a back-up to another method of waterproofing a backpack.

 

Rain Cover

Rain covers have become increasingly popular in the last few years as a method for waterproofing a backpack as they have gotten lighter, cheaper, and more compact with recent technological advancements. Essentially, a rain cover is a thin piece of waterproof material that stretches over the outside of a backpack. There’s really nothing fancy about them – they’re just a piece of nylon or some other waterproof material with an elastic band that tries to keep it attached to the outside of your bag.

The advantage to a rain cover is, as we’ve mentioned, that it’s a lightweight and compact piece of gear that can easily be stowed in a pack until it starts to rain. Indeed, the vast majority of people who use rain covers will only take them out when the rain starts. In fact, many packs now come with a small pocket, specifically designed for a rain cover to be easily accessible during a storm.

The problem with rain covers is that they’re not actually very effective at keeping your pack dry in a big storm. Sure, they start out well, but as the wind picks up and you continue hiking, they usually manage to slide off of your pack during the heaviest part of a rainstorm. Best case scenario, a small amount of your gear gets wet, but worst case scenario, your entire pack gets soaked and your rain cover flew away and is now tangled in a tree somewhere. That being said, many modern packs do have some sort of attachment system to help prevent this from happening, so if you live somewhere that’s particularly windy, that might be a good investment.

Plus, pack covers are not a “one-size-fits-all” piece of gear, regardless of what anyone tells you about their pack cover being “universal.” Sure, you can use that 75L pack cover on your 35L day pack, but eventually, it’ll catch the wind and turn you into a giant umbrella flying in the wind. Thus, for every pack you have, you need to buy a separate rain cover that’s appropriately sized.

Pros:

  • Convenient
  • Small and lightweight
  • Works well in light rain

Cons:

  • Can and do easily fly away
  • You need a different pack cover for every pack size
  • Don’t protect gear during a river crossing

Best use: Light rain and minor storms in non-exposed terrain below treeline, where the risk of flying away is quite small.

 

Pack Liner

grey Osprey pack liner on hardwood floor
Osprey Pack Liner

Pack liners do pretty much exactly what you would think based on their name – they line the inside of your pack. Made from seam-sealed, waterproof materials, pack liners are one of the best ways to protect your gear. Basically, all you need to do is get a pack liner, put in in your empty bag and then pack your gear into the liner/backpack combo. Voila! A waterproof pack awaits.

There are a few different kinds of pack liners out there, but the only kind worth spending money on is one like this from Osprey. While you can certainly buy a plastic bag-type pack liner, then you’re basically spending good money on a glorified garbage bag, which is another method of pack waterproofing we’ll discuss in a bit.

The fabric pack liners, on the other hand, are made from a lightweight waterproof, seam-sealed material (similar to what you’d find in a dry bag) and use the same roll-top closure that a dry bag has for weather protection. They usually come in a rectangular shape, which makes it easier to pack inside a backpack.

One of the best parts about a fabric pack liner is that, unlike the garbage bag method, which we’ll look at next, you can reuse a fabric pack liner until it rips or gets holes in it. If your pack liner ever gets a hole in it, you can always patch it up with some gear repair tape and get back on your way.

Pack liners are waterproof, durable, reusable, and really effective at keeping your gear dry. They do require a financial investment and add a few ounces to your pack weight, but that’s better than getting hypothermia because your down sleeping bag got soaked.

However, pack liners don’t protect the outside of your pack from getting wet like a pack cover does, so you’ll still have a wet backpack at the end of the day, despite the fact that your gear is dry. Additionally, if you have any electronics with you or other really important gear (like that sleeping bag), it’s worth putting these in a second dry bag, just in case you rip a hole in your pack liner during your trip.

Pros:

  • Great at keeping gear dry
  • Reusable and repairable
  • Easy to pack gear into

Cons:

  • Cost money
  • Come in specific size ranges
  • Add a few ounces in pack weight

Best Use: Day hikes and backpacking trips where your gear just can’t get wet.

 

Garbage bag

If you don’t want to invest in a proper fabric pack liner, you can always opt to use a garbage bag as a pack liner instead. To use this method, you’ll want to get yourself two heavy duty compactor garbage bag – one of the ones you’d use for lawn refuse. Then, just line your pack with one of the garbage bags and pack the other into your bag as a back-up, just in case the first one rips.

This quick, simple, and easy method has proven itself time and time again to be incredibly effective at keeping gear dry. Garbage bags are made from waterproof materials, so unless you rip a hole in one, it’ll protect your gear in any weather. Plus, they’re super affordable and you probably already have some lying around your house.

There are a few drawbacks to using a garbage bag, though. First and foremost, they can and do rip, which is why you always want to have a spare on hand if you’re going out for more than a day. Additionally, garbage bags are made from plastic and are purposefully designed to be single use. This means that if you go outside a lot, you’ll be producing quite a bit of waste just from your attempts to waterproof your gear.

Pros:

  • Affordable
  • Quick, simple, and easy
  • Doesn’t add any weight to your pack

Cons:

  • Adverse environmental consequences
  • Can rip somewhat easily

Best Use: Day hikes and backpacking trips where your gear just can’t get wet.

 

Ziploc bags

If you just need to keep a few items dry in your pack, such as your phone or headlamp, you might not need to waterproof your entire backpack. Instead, you could use plastic bags to keep specific items dry.

A standard, resealable plastic bag is a popular choice among people who just need to keep a few pieces of gear dry. If you really want to keep something dry, you can double or triple bag it to keep the water out.

Since resealable bags tend to fall apart after a while and the seal tends to fail, a more durable alternative to a Ziploc bags is a 2mm poly bag. While these don’t have a sealing mechanism, it’s easy enough to tie them off using an overhand knot, at which point, they’re pretty much waterproof unless you send them down a river. The main downside to these bags is they come in huge quantities, so it can be best to find a few friends who want to split a carton with you instead of getting one for yourself.

Moreover, plastic bags have the same negative effect on the environment that a garbage bag has, so it’s not the most eco-friendly option out there. Although they may be cheap in the short run, if you go outside a lot, you might save money by investing in a dry bag alternative.

Pros:

  • Affordable
  • Lightweight
  • Versatile

Cons:

  • Negative environmental consequences
  • Not very durable

Best Use: Keeping small items dry in a backpack

 

Dry Sacks

yellow dry sack filled with gear
Sea to Summit Dry Sack

Similar to Ziploc bags, dry sacks are best used to keep individual items of gear or small sets of gear dry. They come in a wide variety of different shapes, sizes, and materials, so you’ll need to consider precisely what it is you want to keep dry before you purchase one.

What’s important is that you find a dry sack that’s relatively lightweight, like these from Sealine. There are dry bags out there made of a more durable rubbery material that is best used for boating, not hiking as it’s quite heavy. While individual dry bags might not weigh too much, when you have four or five, they start to add up.

Additionally, it’s best not to pack everything you own into separate dry bags and then put it into your pack as this will make it difficult to pack your bag properly. Instead, we recommend using dry sacks for particularly sensitive gear items, like a sleeping bag or phone, and then also using a pack liner to protect all of your gear. Ultimately, for hiking, a dry sack is better for a few smaller items, not everything in your pack.

Pros:

  • Versatile
  • Durable
  • Highly waterproof

Cons:

  • Somewhat expensive
  • Adds weight to your pack

Best Use: Keeping small items dry in a backpack

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