A reed diffuser is the least technological thing in your house, and it's quietly clever.
Capillary action, mostly
The reeds are porous — full of microscopic channels running end to end. Liquid climbs those channels on its own, against gravity, because the oil is more attracted to the reed's inner surface than it is to itself. The same reason a paper towel pulls water upward when you dip a corner in it.
Oil travels up, reaches the exposed length above the bottle, and evaporates from there into the room. No heat, no power, no moving parts. The bottle is a reservoir and the reeds are a very slow pump.
Why it's continuous rather than dramatic
A candle gives you scent when it's lit and stops when it isn't. A diffuser has no off switch, which is both its advantage and its limitation. It won't fill a room quickly, and it was never going to — it's designed to hold a low, steady presence for weeks rather than to make an entrance.
What that means practically
More reeds means more exposed surface, which means faster evaporation and a stronger throw — and a bottle that empties sooner. Fewer reeds, the reverse. That's the only dial you have, and it's a real one. Start with all of them; pull two out if it's more than the room needs.
Warmth and moving air both speed evaporation up, which is the same principle we wrote about for candles and mists in winter. A diffuser near a sunny window or an open passage works harder and runs out faster than one on a shelf in a still, cool room.