By Marcus Hale, Lead Pack Research Editor · Published September 14, 2026, 6:03 PM ET
Direct Answer
Keep gear dry inside a backpack by packing everything inside a sealed pack liner — a trash compactor bag or purpose-built roll-top liner — rather than relying on the pack's own fabric and zippers. Add a rain cover over the outside for wind and exterior-lashed gear, and double-bag electronics for extra protection.
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In plain English
No backpack is truly waterproof, because rain sneaks in through stitching and zippers. So the trick is not to make the pack waterproof. It is to put a waterproof bag inside the pack and keep your things in that bag.
Picture a cardboard box in the rain with a plastic bag inside it. The box gets soggy, but whatever is in the plastic bag stays dry. A heavy trash bag or a special roll-top liner does the same job in a backpack.
For the most important things, like your sleeping bag, spare warm clothes and your phone, add a second small waterproof bag. A cover over the outside of the pack is a nice extra, but the inside bag is what really protects your gear.
The most dependable way to keep gear dry doesn't rely on the pack itself being waterproof, since no hiking backpack shell fully is.
The core method: a pack liner
Line the entire main compartment with a heavy-duty bag before adding any gear, then twist or roll the top shut and fold it over before closing the pack. A thick trash compactor bag works for most trips; a purpose-built roll-top liner from a brand like Sea to Summit holds up to more repeated use. Because the seal is on the inside, it doesn't matter whether the pack's own seams or zippers leak.
Add a rain cover for the outside
A rain cover, pulled over the loaded pack before rain starts, protects the shell fabric and anything strapped to the outside — a sleeping pad, wet jacket, or trekking poles in a side pocket. It can't cover the back panel against a hiker's back, which is why it works best paired with a liner rather than used alone.
Double up on electronics
Phones and GPS units: a dedicated waterproof pouch with a roll-top or clip seal, kept accessible in a hip-belt pocket
Cameras and battery packs: a zip-top freezer bag placed inside the main pack liner
Everything else: inside the liner by default — exterior pockets, even zippered ones, are the least protected part of any pack
Reproof the shell periodically
A DWR treatment on the face fabric, renewed when water stops beading and starts soaking in, slows how fast the shell itself gets wet and heavy — a smaller factor than the liner and cover, but part of a complete system.
Why the inside layer matters most
Pack fabric is usually coated, but REI notes that water can still seep through seams and zippers,1 and Deuter says sustained downpours can let moisture in through zippers and seams even when the fabric itself is waterproof.2 An inside liner doesn't care about either weak point, which is why it is the core of every reliable system.
Covers and liners also behave differently in wind. REI says waterproof stuff sacks inside the pack are an alternative to a rain cover and can work better in wind.1 Deuter suggests dry bags inside for alpine use, where they keep straps accessible, and a rain cover for hiking packs.2 Using both covers the most situations.
Protect warmth first
The gear worth the most protection is whatever keeps you warm, because being wet and cold is dangerous. The CDC says hypothermia can develop even in cool temperatures above 40°F if a person gets chilled from rain, sweat or cold water.3 The CDC Yellow Book adds that in cool conditions, the priority is staying dry by layering and changing out of damp clothing quickly.4
Material choice matters too. The National Park Service notes that cotton absorbs water into its fibers and stays wet a long time.5 A dry sleeping bag and a dry synthetic or wool layer sealed in their own bags give you a safe fallback if everything else gets wet.
How waterproof is the liner?
Purpose-built liners and dry bags are sometimes sold with a hydrostatic head rating. Sea to Summit explains that the number is the height of water column a fabric withstands; if water breaks through at 1 meter, the rating is 1,000 mm.6 A trash compactor bag has no rating, but for gear that sits inside a pack rather than under water, a thick, intact bag with its top twisted and folded does the same job. Check it for holes before each trip.
Keeping gear dry also keeps weight down. A liter of water has a mass of about one kilogram,7 so a sleeping bag and clothes that soak up even a liter add more than two pounds you have to carry for the rest of the day.
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