Do You Need a Pack Liner for a Waterproof Backpack?

More and more ultralight backpacking packs are being made with waterproof materials like Dyneema Composite Fabrics (DCF), Ultra, Liteskin, EcoPak, and XPac. These fabrics absorb very little water and are bonded with a waterproof layer that prevents them from being soaked through when it rains and making your gear wet. Some are even seam-taped by manufacturers, so water can’t leak through the needle holes that are created in the pack fabric when the shoulder straps or hip belts are sewn onto a backpack.

Naturally, the question arises whether you still need a pack liner, like a plastic trash compactor bag, a nylofume plastic bag, or a high-volume DCF dry sack to protect your gear from getting wet if it rains.

Material Failure

While Dyneema Composite Fabrics (DCF), Ultra, Liteskin, EcoPak, and XPac are quite durable and abrasion-resistant, you can still wear a hole in them, especially on the bottom where they rest on the ground. A pack liner can keep your gear dry when the material starts to break down, leak, and then fail.

Seam-taping is also not foolproof. It can leak under pressure if you accidentally submerge a backpack or it falls out of your packraft and into the water. Seam tape also fails over time, with a lot of folding, scrunching, and rolling, especially in ultralight roll-pack backpacks.

Multiple Uses

But pack liners also have multiple uses beyond keeping the gear inside your backpack dry from rain.

For example:

• Pack liners like the Exped Schnozzel can be used as inflation bags for blowing up air mattress pads from Exped or Sea-to-Summit.
• For keeping wet gear and clothing separate from dry gear and clothing inside your backpack.
• To keep your gear dry from a leaky hydration system. Reservoirs, hoses, or gaskets leak eventually or you forget to close the top tightly and flood the inside of your pack. I’ve had a 3L reservoir empty in a full backpack and the only thing that saved my bacon was the pack liner.
• To store wet hiking shoes or a water filter inside your sleeping bag/quilt on very cold nights to prevent them from freezing while still keeping your sleep insulation dry.
• Inside a sleeping bag as a vapor barrier liner for your lower body to stay warmer in freezing temperatures.
• As a carry-on bag, when you’re forced to check your backpack for air travel.
• As a makeshift poncho or vapor barrier booties, with the help of a pair of scissors.
• There are even more creative ways to cut them up and use them in an emergency.

No Substitute

If you consider the attributes that make a waterproof pack liner valuable and unique, the one thing that stands out is its volume. It’s big enough to hold anything in your other stuff sacks with room left over. It’s often large enough to provide shelter or rudimentary clothing for a person in an emergency. There’s really nothing that comes close to its degree of utility in your backpack and there’s no way to backfill for it with any of your other stuff sacks or gear.

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