Dry Bag vs Dry Bag Backpack: Which Should You Buy?
26 October 2026
The short answer: buy a plain dry bag if you are stowing kit somewhere — in a kayak hatch, on a boat, under a bungee — and buy a dry bag backpack if you have to carry it any distance on your back. Both keep water out the same way. The difference is entirely in how you move with them.
It sounds obvious written down, but it is the question we get asked most, and getting it wrong is annoying in a specific way: a 30-litre sack with one shoulder strap is miserable on a mile walk to the beach, and a padded expedition pack is overkill for something that spends its life clipped inside a cockpit.
What is the actual difference?
Nothing about the waterproofing. Every Ultra Dry bag, plain or backpack, is the same welded tube of premium-grade 500D PVC, roughly 0.5 mm thick, closed by the same roll-top. Water gets in through the opening or not at all, and that is down to how you roll it rather than which model you bought.
What changes is the carrying system:
- A plain dry bag has one removable shoulder strap. It stows, clips and stuffs into spaces. You carry it over a shoulder for a few minutes at a time.
- A dry bag backpack has two straps, so the weight sits on both shoulders and your hands stay free. Above 30 litres it also gains padding, a waist strap and a back panel, because at that point the load needs managing rather than just holding.
When a plain dry bag is the right choice
Pick a plain bag when the bag spends most of its time not being carried. Kayaking and canoeing is the clearest case: a 5 or 10 litre bag lives in the cockpit or clipped to a deck line with your phone, keys and a dry layer inside, and never goes on your back at all. The same applies on a sailing boat, in the back of the car at a swim spot, or strapped to the front bungees of a paddleboard.
It is also the right answer for the thing most people actually want, which is somewhere trustworthy to put valuables. Our 5 litre bag comes with an extra-long shoulder strap, adjustable to 48 inches, which is long enough to wear across the body under a buoyancy aid.
When a dry bag backpack is the right choice
Pick a backpack the moment there is a walk involved. Sea swimmers parking at the top of a cliff path, paddlers carrying kit from the car park to the slipway, anyone cycling or commuting, and — the big one — Duke of Edinburgh groups carrying everything they own for three days.
The test is simple. If you will be carrying it for more than about ten minutes, or if you need your hands for anything (a board, a paddle, a child, a gate), you want two straps.
Not all dry bag backpacks are the same
This is the part that is genuinely worth knowing before you buy, because the word “backpack” covers three quite different things in our range.
Two straps, no padding — the 20 litre
The 20 litre comes with two removable shoulder straps, so it works as a backpack when you need it and as a plain sack when you do not. There is no padding and no waist strap. For a day’s worth of kit over a reasonable distance that is perfectly comfortable, and the removable straps make it the most flexible bag we sell.
Padded shoulders and a sternum strap — the 30 litre
The 30 litre has padded shoulder straps and an adjustable sternum strap across the chest, which stops the straps sliding outwards as you walk. It is the natural choice for a long day out where you are carrying more than a change of clothes.
A proper back system — the 35 and 55 litre
These two are built for being worn all day, and they have things the 30 does not:
- A padded back panel with breathable mesh. Twin padded sections sit between you and the bag, so hard or awkwardly packed kit does not dig into your back, and air can move behind the pack on a long carry.
- Adjustable shoulder, chest and waist straps, so the weight moves off your shoulders and onto your hips — which is the single biggest comfort difference on a multi-day carry.
- A splash-proof zip pocket with a window, so you can see where the thing you need actually is without unrolling the whole bag.
- Reflective detail, which matters more than you would think on a lane at dusk.
If you are kitting out a Duke of Edinburgh expedition, this is the distinction that counts. The 30 litre will hold the kit; the 35 will hold the kit and still be bearable on day three.
Do the straps make a backpack less waterproof?
No, and it is a fair thing to wonder, because stitched-on straps sound like holes. The straps attach to the outside of the welded body, so the waterproof part of the bag is not pierced. A 35 litre backpack closed properly is exactly as dry inside as a 5 litre sack closed properly.
Both are 100% waterproof in the sense that matters — the body does not leak and the rolled top seals — and both are IPX6 rated, which is worth two minutes of reading if you want to know what that covers. The short version: rain, spray, waves over the deck and a capsize are all fine, and the trapped air means the bag floats. What no roll-top is built for is being left underwater.
Dry bag or backpack: the quick version
| You are doing this | Buy this |
|---|---|
| Keeping valuables dry in a kayak or on a boat | 5L or 10L plain dry bag |
| Paddleboarding with a change of clothes | 10L or 20L |
| Beach day, swim spot, short carry from the car | 20L backpack |
| Long day out, hands free, bigger load | 30L padded backpack |
| Duke of Edinburgh, expeditions, all-day carrying | 35L — padded back panel |
| Multi-day trips, or carrying for two | 55L |
Still deciding?
If it is the size rather than the style you are unsure about, our dry bag size guide compares all six side by side with current prices, and there is a longer guide to choosing a size if you want the detail.
Whichever you choose, a waterproof phone case comes in the box, every bag carries our 5-year guarantee, and we ship across the UK. Our bags are carried by UK International Search and Rescue teams on real deployments, which is the endorsement we are proudest of.
Browse the waterproof backpacks →
Browse the plain dry bags →