In Vietnam the rain does not ask permission, and it comes sideways. Zips leak, seams wick, and the backpack you trusted soaks your laptop in the time it takes to find shelter. Dry bags solve rain at the luggage level.
Why dry bags beat “waterproof” bags
A roll-top dry bag seals by folding: three folds and a buckle, no zip to fail, no seam tape to lift. Electronics, documents, spare clothes and anything that must arrive dry live in dry bags — inside whatever outer luggage you use. Layering is the principle: the outer bag takes abrasion, mud and theft exposure; the dry bag inside takes water. A top box that has sealed for two monsoons will still admit water at a worn gasket — the box article is top-boxes-racks-motorbike-vietnam — and the liner inside makes that failure harmless.
Sizes and colours
Small 2–5 litre roll bags fit phones, chargers, documents and a change of shirt under a scooter seat. Medium 10–20 litre bags line backpacks and saddlebags — the backpack-versus-saddlebag trade-off in backpack-vs-saddlebags-motorbike keeps working in the rain with the right liner. For trips, 30+ litre duffel-style dry bags strap to rear racks. Bright colours beat black: a bag that will be opened roadside in low light should be visible, and black roll bags vanish at dusk — visibility thinking applies to luggage too.
What still goes wrong
Users seal bags badly: fold at least three full turns, buckle, and test by pressing the air out — air escaping means water entering. Fabric dries, but the contents must not already be damp when sealed: humid Vietnam turns a sealed damp t-shirt into a mould farm. And do not confuse water-resistant with waterproof: a resistant bag handles spray and drizzle, a dry bag handles submersion at a flooded intersection — the riding context is riding-motorbike-heavy-rain-vietnam.
Securing and loading
Load discipline follows the same physics as any luggage: heavy low, forward, and strapped per carrying-luggage-motorbike-safely-vietnam. Dry bags are slippery when wet — use the strap points, never bungee over the barrel alone, where a wet strap can walk off.