Packing waterproof: dry bags and pack liners

A backpack is made of fabric, seams and zips. Even if the fabric is coated, water eventually gets in during prolonged rain: through the needle holes of the seams, through zips and at places where the coating is worn. It is worst at the back, because the rain cover is open there and water runs down from the jacket.

A roll-top dry bag seals because the opening is rolled over several times. Each roll is another barrier the water would have to get past. The entry recommends rolling tightly at least three times. Before that, press out the air and flatten the opening so that no creases or folds leave a gap. Then close the buckle so the roll does not open again.

Besides protecting against wet, dry bags keep things organised. When sleeping gear, clothing, kitchen and first aid are in their own bags, you find everything faster – even more so if you use different colours. And you keep wet things apart from dry ones.

The simplest and most reliable solution is one large liner that lines the whole pack. This can be a purpose-made waterproof bag or a heavy-duty bin bag. You put it into the pack and pack everything into it. At the top you twist or roll it closed.

Whatever matters most you protect twice: the sleeping bag, spare clothing, documents and electronics also go into their own dry bags or sealed pouches. The sleeping bag and warm clothing are your warmth reserve – they must stay dry even when everything else is wet.

Wet things never go into the dry section. Put a wet tent or wet clothing on the outside of the pack or in a bag of its own. Sharp objects such as stove parts, tent pegs or a knife should not rest directly against a dry bag, because they can wear through it.

A wet sleeping bag and wet spare clothing can become dangerous in the cold, because you then have no way to warm up after a wet day. So the rule is: the warmth reserve is always packed most securely, even if that means a few grams more weight.

Most dry bags are only splash-proof or can survive brief submersion, but not lying underwater for a long time. What your dry bag can really do is stated in the manufacturer's information. On canoe and boat trips where capsizing is possible, you should know this beforehand and protect important items additionally.

When crossing a stream, the pack can end up in the water if you slip. Well-packed things then stay dry. Whether a stream crossing is safe at all is a quite separate question, though – if in doubt, look for another spot or turn back.

Dry bags wear out over time, especially at creases where they are folded again and again. A small hole is enough to let water in. So check them before a trip and now and then in between.

The test is simple: fill the dry bag with air, roll it closed as usual, close the buckle and squeeze it. If air escapes anywhere you will hear or feel it – there is a hole or a leaking seam there. Small holes can often be repaired with a suitable patch; a badly worn bag is better replaced.

After a wet trip, let dry bags dry open before you put them away. Otherwise mould can form inside. A bin bag as a liner is cheap but more fragile; take a second one as a spare just in case.

On a rainy hike, the liner is often enough on its own, combined with a separate dry bag for the sleeping bag and spare clothing. On snow trips the same method protects against meltwater that gets into the pack when you set it down in the snow.

Paddlers have long used roll-top dry bags because on the water you must always expect spray and sometimes a capsize. In a go bag too, documents, medication and electronics are well kept in a sealed pouch – for example during an evacuation in rain or floods.

Mountaineering handbooks recommend protecting pack contents from wet with liners or plastic bags. The method is simple, cheap and one of the most effective safety measures you can take when packing.