Most two-wheeler collisions in city traffic begin the same way: the other road user says they looked and did not see. A rider is a narrow object in a street full of moving metal, and anything that makes you visible earlier gives a bus or a turning car more seconds to register you. A hi-vis vest is the cheapest, hottest-debated way to buy those seconds.
Fluorescent and reflective are two different things
Fluorescent yellow-green converts UV into extra visible light, so it looks abnormally bright — in daylight. After dark it is just a yellow rag. Reflective material, usually grey in daylight, bounces headlight beams straight back at drivers — in darkness it is the thing that works. A good riding vest has both: fluorescent panels for the day, wide reflective bands for the night. Cheap vests that are all colour and no retro-reflective banding are half a product — the same logic applies to bike-level reflectives in reflective-stickers-motorbike-visibility.
When it genuinely helps
Peak effectiveness is exactly the conditions Hanoi riders know well: dusk and dawn, drizzle, and fog, when contrast collapses and everything in a mirror becomes grey — see fog-and-low-visibility-riding-motorbike-vietnam. It also matters in the dry-season haze, when dust softens every outline: dust-dry-season-riding-vietnam. At night in the rain, a reflective vest over your jacket is one of the few things that still reads at a glance through a windscreen streaked with water — the same low-visibility window where drivers misjudge distance, as in after-rain-slippery-roads-motorbike.
What it does not do
A vest does not make right of way appear. Drivers must still be looking at the moment you matter, and hi-vis does not protect against the merge you did not anticipate. It is a layer of margin, not a strategy — positioning, speed management and eye contact remain the core skills.
Choosing one worth wearing
Look for wide horizontal reflective bands (thin piping is decoration), a snug fit that does not balloon at speed, mesh or lightweight fabric for the heat, and enough durability to survive being pulled on over a jacket hundreds of times. An oversized vest that flaps is noise, fatigue and a distraction — and riders who hate the flapping stop wearing it, which zeroes the benefit. Wear it when it matters most: night rides, rain, fog and highway stretches.