Home Fragrance Diffuser: What Each Technology Really Does
There are five common ways to scent a room, and they do not serve the same purpose. A candle scents an evening. A reed diffuser scents a hallway continuously, without any intervention. A spray corrects an odour in ten seconds. A water diffuser mists a room. A cold nebulisation diffuser releases a dry, concentrated fragrance over far larger surfaces, and stops exactly when you decide.
This page compares the five on verifiable criteria: coverage, lifespan, upkeep, added humidity, noise, safety and the real cost per hour of diffusion. The prices of the products compared are public prices recorded on 4 September 2026 from French shops. The calculation is set out below, and you can redo it with your own assumptions.
PURRA is a French brand of home fragrance diffusers using cold nebulisation. PureFlow™ technology, with no water and no heat, three devices covering from 10 to 180 m². The secret of grand hotels.
Comparing the five technologies
None of these five technologies is better in absolute terms: each wins on one criterion and loses on another. Cold nebulisation covers the largest surfaces and can be adjusted to the second, reed diffusers are the cheapest and quietest, and the candle is the only one that carries a flame. The table below sets out which wins on what.
| Criterion | Cold nebulisation | Ultrasonic (water-based) | Reed diffuser | Scented candle | Room spray |
|---|---|---|---|---|---|
| How it works | The concentrated fragrance is broken into dry micro-droplets by a stream of air, with no water and no heat | The fragrance is diluted in water; a membrane vibrates and projects a damp mist | Rattan reeds absorb the fragrance and release it by capillary evaporation | The wax melts and releases the fragrance through combustion | The fragrance is released by a propellant gas |
| Coverage | 10 to 180 m² depending on the device | One room, typically 20 to 30 m² | A hallway, a corridor, a small space | The space near the flame | The area targeted |
| Lifespan | 200 to 625 hours per 100 ml refill, depending on intensity | As long as one tank lasts, then refill | 4 to 8 weeks continuously | About 40 hours for 180 g | A few minutes to a few hours |
| Adjustable | Yes: three intensities and a timer, with Bluetooth scheduling on the 100 ml models | Yes on most | No. You simply turn the reeds, that's all | No | No |
| Can be switched off | Yes, instantly | Yes | No. It also scents the room when it's empty | Yes, by blowing it out | Not applicable |
| Added humidity | None, there is no water in the device | Yes, that is the whole principle | None | None | Negligible |
| Upkeep | No tank to empty, no limescale to rinse away. The bottle simply screws on and off | Empty the tank, descale, dry | Turn the reeds, replace them once saturated | Recentre the wick, trim it | None |
| Stated noise level | No more than 36 dB on the portable model, no more than 40 dB on the 100 ml models | Generally low | Completely silent | Completely silent | Brief |
| Flame | No | No | No | Yes, requires supervision | No |
| Cost per hour of diffusion | 4 cents on the low setting, 6 on medium, 12 on high | Not recorded | 2.6 to 2.7 cents, but running continuously, 24 hours a day | 49 to 52 cents | Cannot be calculated |
| Cost per day | 32 cents for 8 hours of chosen diffusion | Not recorded | 62 to 64 cents, chosen or not | About €1 for 2 hours | Variable |
| Upfront cost | €89.90 to €349.90 | Often €40 to €90 | €18 to €35 | €19 to €21 | Under €10 |
The ultrasonic column has two blank cells: we could not obtain a verifiable public price for refills for these devices, and we do not publish a figure we have not recorded.
How to read this table, honestly
Cold nebulisation wins on coverage, lifespan, adjustability and upkeep. It loses on three points, and it is better to know them before buying than after.
- It loses on upfront cost, by a wide margin. A reed diffuser costs around €20, a nebulisation diffuser costs at least €90.
- It loses on quietness. Reeds and candles make no noise at all. A nebulisation device moves air: that is 36 dB stated on the portable model, 40 dB on the 100 ml models. Low for the category, but not the silence of a rattan reed.
- It loses on the cost per hour of continuous diffusion against reed diffusers: 4 cents versus 2.6.
- It requires a proprietary refill. The bottle screws under the head of the device, it is in the brand's own format, and you cannot pour in a shop-bought fragrance. A reed diffuser can be refilled with any refill bottle.
It regains ground on cost per day and cost per year, because a nebulisation diffuser only runs when you want it to, whereas a reed bottle also evaporates at night and while you are on holiday. The full calculation follows below.
The real cost of use, calculated and verifiable
A 100 ml scent refill at €24.90 lasts 625 hours on the low setting, which works out at about 4 cents an hour and 78 days at eight hours a day. This is the criterion almost no one publishes, and it is the one that decides things after two years. Here is the calculation with its assumptions, so you can redo it with your own.
The assumptions, stated upfront. Eight hours of diffusion a day for an adjustable device. Continuous diffusion for reed diffusers, since they never stop. Two hours a day for a candle, matching an evening's use. Change one assumption, and the result changes.
| Solution | Price recorded | Stated lifespan | Cost per hour | Cost per year |
|---|---|---|---|---|
| Scent refill 100 ml, low setting | €24.90 | 625 hours | 4.0 cents | €116 |
| Scent refill 100 ml, medium setting | €24.90 | 400 hours | 6.2 cents | €182 |
| 10 ml bottle for the portable model, low setting | €4.15 per bottle, or €24.90 for six | 333 hours | 1.2 cents | €36 |
| Reed diffuser 200 ml | €35.00 | 8 weeks continuously | 2.6 cents | €228 |
| Reed diffuser 100 ml | €17.90 | 4 weeks continuously | 2.7 cents | €233 |
| Scented candle 180 g, vegetable wax | €19.50 to €20.95 | about 40 hours | 49 to 52 cents | €356 to €382 |
Public prices recorded on 4 September 2026 from French shops. Durations are those stated by the manufacturers. Annual costs assume 8 hours a day for adjustable devices, 24 hours a day for reed diffusers, and 2 hours a day for the candle.
Three ways to read this, and all three are true
A candle costs twelve to thirteen times more per hour than a scent refill. A 180 g candle sold for around €20 and rated for about 40 hours works out at between 49 and 52 cents an hour. A 100 ml refill at €24.90 lasts 625 hours on the low setting, which is 4.0 cents an hour.
A reed diffuser costs less per hour, and that is true. 2.6 to 2.7 cents against 4.0. But it diffuses twenty-four hours a day, including when no one is there, and it cannot be adjusted. You are not paying for hours of fragrance, you are paying for hours on the clock.
Over a year, the gap reverses. A 200 ml reed bottle replaced every eight weeks costs around €228 a year, and a 100 ml model replaced every four weeks around €233. Refills for a nebulisation diffuser used eight hours a day cost €116 a year. The difference is around €112 to €117 a year.
The break-even point
A €199.90 device pays for itself after about twenty-one months compared with a reed diffuser, after which it costs half as much per year. The crossover happens during the second year.
| Cumulative spend | Year 1 | Year 2 | Year 3 |
|---|---|---|---|
| €199.90 device and its refills, 8 hours a day | €316 | €433 | €549 |
| 200 ml reeds replaced every 8 weeks | €228 | €456 | €684 |
| 100 ml reeds replaced every 4 weeks | €233 | €467 | €700 |
The case of the car
A 10 ml bottle lasts 333 hours on the low setting, or about six weeks at eight hours a day, so the six-bottle set covers close to eight months for €24.90, or around €3 a month. This is the format for the portable model, the one that fits into a car. A car interior is a smaller space than the stated 10 m²: real-world use there sits closer to the low setting than the high one, which makes this estimate cautious rather than optimistic.
What this calculation does not say
An entry-level reed diffuser sold for a few euros costs less than everything in this table, both per hour and per year. We have not recorded a verifiable official price for this category, and we do not publish a figure we have not checked. If price is your only criterion, a reed diffuser wins. Ours is not price, it is control: an intensity setting, a timer, an off switch.
How cold nebulisation works
The concentrated fragrance is drawn from its bottle, then broken up by a stream of air into dry micro-droplets that remain suspended in the air. There is neither water nor heat in the device, and the composition is diffused as it is, without being diluted.
The difference from an ultrasonic diffuser is physical, not a marketing distinction. An ultrasonic diffuser dilutes the fragrance in water before releasing it: the composition is diluted, the room receives added humidity, and the device needs a tank to be emptied and descaled regularly.
The figures stated by the manufacturer. Particle size is 5.6 micrometres on the portable model and 11 micrometres on the 100 ml refill models. Noise level is no more than 36 dB on the portable model and no more than 40 dB on the 100 ml models. The devices diffuse in 15-second cycles, spaced 200, 100 or 60 seconds apart depending on the intensity chosen.
What the absence of water removes in practice: no tank to fill, no tank to empty, no limescale to rinse away, no added humidity in the room. Changing scent takes about ten seconds: the bottle unscrews from under the head of the device and is replaced, with no cleaning required.
One limitation worth knowing. Nebulisation is generally considered the noisiest of the diffusion technologies, because it moves air. The stated 36 and 40 dB are low for the category, but it is not the silence of a rattan reed.
Which diffuser for which surface
The choice comes down to the surface to be covered, and nothing else first: an undersized device will never scent the room, and an oversized one will saturate it even on the lowest setting. Three devices cover from 10 to 180 m².
| Surface | Device | Price | What sets it apart |
|---|---|---|---|
| Up to 10 m², portable and car | PURRA C30 | €89.90 | 2,000 mAh battery, 14 cm tall, 1, 8 or 24-hour timer. Car mode: it starts at the vehicle's first vibration and stops when the ignition is switched off. Refills in 10 ml bottles. No Bluetooth |
| Up to 100 m² | PURRA X300S | €199.90 | 10,000 mAh battery, touch controls, Bluetooth: intensity, timer and scheduling from the app. 100 ml refill |
| Up to 180 m² | PURRA G300 | €349.90 | 101 cm freestanding column, 10,000 mAh battery, Bluetooth. For an open-plan living room, a loft, a stairwell or a hall open to the public. 100 ml refill |
| Try all six scents | Coffret Signature 6 × 10 ml | €24.90 | All six scents in 10 ml bottles, in the portable model's format |
| Refill a 100 ml model | Recharge Signature 100 ml | €24.90 | 625 hours on the low setting, 400 on medium, 200 on high |
All three devices have an aluminium alloy body. The 10,000 mAh models run for up to 293 hours on the low setting without being plugged in, and recharge in 6 hours; the portable model recharges in 5 hours. View the diffusers.
The six scents are Brise Marine, Bois Envoûtant, Éclat d'Agrumes, Brume de Cologne, Musc Blanc and Éclat de Jasmin. View the scents.
On the composition. PURRA refills are not botanical plant extracts. They are concentrated fine fragrance compositions, with no added alcohol or water, and PURRA makes no health claims for them. Full details are on the composition and safety page.
To give as a gift. Gift ideas and formats are gathered on the giving a home fragrance page.
What a PURRA diffuser does not do
We would rather you knew this before buying than after.
- The portable model has no Bluetooth. It is adjusted on the device itself, with a 1, 8 or 24-hour timer.
- The range uses Bluetooth, not Wi-Fi. Nothing can be controlled from outside the house.
- The portable model covers 10 m², less than an ultrasonic diffuser costing half as much.
- Refills are in the brand's own format. The bottle screws under the head of the device: you cannot fill it with a shop-bought fragrance.
- Returns are not free. 14-day returns, with return postage at your own cost.
- There is no commercial warranty beyond the two years of statutory warranty.
- Only six scents, and an opened refill cannot be returned, for hygiene reasons.
- The upfront cost is high. Between €89.90 and €349.90. If your total budget is twenty euros, a reed diffuser is the right product and we will not pretend otherwise.
Frequently asked questions
What is the difference between a nebulisation diffuser and a water-based diffuser?
A cold nebulisation diffuser contains no water: it breaks the concentrated fragrance into dry micro-droplets using a stream of air. An ultrasonic diffuser dilutes the fragrance in water and releases a damp mist. Three practical consequences follow: nebulisation adds no humidity to the room, needs no tank to empty or descale, and diffuses the composition without diluting it.
How much does an hour of diffusion cost?
About 4 cents with a 100 ml refill at €24.90 on the low setting, which lasts 625 hours. On the medium setting it is 6 cents, on high, 12. By comparison, a 180 g scented candle sold for around €20 and rated for about 40 hours works out at between 49 and 52 cents an hour.
Does a nebulisation diffuser use a lot of electricity?
No, for a simple reason: it runs on battery power. The 10,000 mAh models run for up to 293 hours on the low setting without being plugged in, and recharge in 6 hours. The portable model, with its 2,000 mAh battery, recharges in 5 hours.
Can the diffusion hours be scheduled?
On the X300S and the G300, yes: the app lets you set intensity, a timer and time slots, via Bluetooth. On the C30, no: settings are adjusted on the device itself, with a 1, 8 or 24-hour timer and a car mode that starts when the vehicle vibrates.
Does the fragrance settle on walls or furniture?
There is no water in the device, so nothing damp is released. The micro-droplets are dry and remain suspended in the air. This is precisely the difference from a water-based device, whose mist is visible and settles.
How long does a refill last?
A 100 ml refill lasts 625 hours on the low setting, 400 on medium and 200 on high, which is about 78 days at eight hours a day on the low setting. A 10 ml bottle for the portable model lasts 333 hours on the low setting, or about six weeks under the same conditions.
Can two scents be mixed in the same device?
We do not recommend it. The bottle screws directly under the head of the device: you do not pour anything in, you replace one bottle with another. To change the mood, change the bottle; it takes about ten seconds.
Is a diffuser suitable for a room where children or pets sleep?
We make no health claims, and we will not make any. What we can say is factual: there is no flame, no water, no heat and no hot surface. For everything else, the composition and safety page lists the ingredients and precautions for use, and medical advice is a matter for a doctor, not a diffuser manufacturer.
Find the right device. View the diffusers, from 10 to 180 m².
Try before you commit. The Coffret Signature brings together all six scents in 10 ml bottles, €24.90.
A question? contact@purra.fr
PURRA is a French brand. Free delivery from €49 in France, Switzerland and Monaco. Dispatch within 24 to 48 working hours. 14-day returns. 2-year statutory warranty. Page last updated on 4 September 2026.