Airflow, Not Wattage, Is What Actually Dries Hair

Most hair dryer marketing talks about heat. In practice, a good dryer is a machine for moving a large volume of air quickly, and the heat is a secondary setting that mostly exists to finish the job. Once you understand that distinction, the difference between models stops being mysterious — and you can work out which one you actually need.

Why airflow matters more than wattage

Water leaves hair by evaporation, and evaporation is driven by air moving across the surface. The faster you replace the saturated air sitting against the hair with fresh, drier air, the faster the water goes. Wattage tells you how much power the machine draws; litres per second tells you how much air it actually moves. Those are not the same number.

For reference, here is how the Dyson range compares:

• HD07 Supersonic™ — 13.3 l/s from a V9 motor at up to 110,000 rpm, 1,600W, 4 heat settings including cold shot, 3 speeds.
• HD16 Supersonic Nural™ — the same airflow philosophy with scalp protection and attachment memory added.
• HD17 Supersonic r™ — 12.5 l/s, 1,700W, and a much smaller body: 30% smaller and 20% lighter than the original.
• HD18 Supersonic r™ Professional — 12.4 l/s, 1,700W, 12.5 ft cord, 325 g body, built for salon use.
• Supersonic™ Travel — 110,000 rpm digital motor, universal 100–240V, 32% smaller and 25% lighter than the full-size dryer.

Notice that the HD07 still has the highest airflow figure of the group. It is also the oldest. That is not an accident: the newer machines trade a little raw volume for a dramatically smaller, lighter, quieter body. If your arm gives out halfway through a blow-dry, 12.5 l/s in a 0.86 kg body will get your hair dry faster than 13.3 l/s in a 1.8 lb body, because you will actually finish.

What intelligent heat control actually does

The useful thing a modern dryer does with its heating element is not “get hotter” — it is “stay steady.” Hair is damaged by temperature spikes, and a basic dryer cycles: the element heats up, the thermostat cuts out, the temperature drops, the element comes back on. The average might be fine while the peaks are not.

Dyson’s answer is continuous measurement. The HD07 reads air temperature 40 times a second; the Travel dryer reads it over 100 times a second. The Airstrait goes further and regulates its airflow temperature up to 16 times a second using glass bead thermistors in both arms. The practical result is that the number on the display is close to the number reaching your hair.

For context on why that matters: a 2019 study in the Journal of Cosmetic Dermatology found the denaturation temperature of virgin hair keratin to be around 237°C (about 460°F), and that heat damage shows up as bubbles inside the fibre at temperatures well below that — the visible signature of water boiling into steam inside the hair. You are not going to reach 237°C with a hair dryer. You can absolutely reach it with a flat iron.

Attachments: what each one is actually for

A dryer on its own is a blunt instrument. The attachment is what turns airflow into a shape.

• Concentrator — a narrow, flat outlet that keeps the airstream together over distance. Air lands where you aim it instead of dispersing. This is the default for a controlled blow-dry.
• Smoothing nozzle — wider and flatter. It smooths by direction rather than by heat: air moving down the hair shaft lays the cuticle flat, while air hitting from every angle lifts it. That is why technique matters more than temperature with this one.
• Diffuser — spreads and slows the airflow so curls dry without being blown out of their pattern, and the prongs lift roots for volume. Our Fabmira 6-inch diffuser widens the bowl from the standard 5.3 inches to 6, so each pass covers more hair.
• Wide-tooth comb — detangles and lengthens as it dries, mostly for textured hair.

One warning worth repeating every time: attachment fittings are not universal. The Supersonic™ and Supersonic Nural™ share an interface; the Supersonic r™ (HD17/HD18) uses a different one; the Airwrap™ uses a third. Check the model code on the handle before buying anything, because a mismatched fitting is the single most common reason an accessory gets returned.

Which dryer for which person

Buy the HD07 if you want the proven model with the widest airflow and the most established track record, and you are happy with a heavier body and an 8.6 ft cable. It remains the reference point.

Buy the HD16 Nural™ if you want scalp protection and the convenience of the dryer remembering which setting belongs to which attachment. It is the middle of the range and the easiest recommendation for most home users.

Buy the HD17 Supersonic r™ if arm fatigue is the thing that makes you stop halfway through, or you have long, thick hair that takes a long time to dry. The smaller, lighter body is the entire argument.

Buy the HD18 Professional if you work behind a chair. A 12.5 ft cord means you can move around a client without repositioning your station, and a spare inner filter in the box means a clogged filter does not cost you an appointment.

Buy the Supersonic Travel if you fly. It is the only dryer in the range that adapts automatically to 100–240V, and it takes the same attachments as your dryer at home.

Two habits that matter more than the model

Clean the filter monthly. The intake at the base of the handle is the only thing between the motor and every bit of dust, hair and styling product in the room. A clogged cage does not just reduce airflow — it makes the motor work against a restriction, which is why the first symptoms are a dryer that feels weak, gets louder, or cuts out mid-dry. Wipe both the outer cage and the inner mesh with a soft, dry cloth.

Finish with cold shot. It is the step most people skip. A blast of unheated air closes the cuticle and sets the shape, and it is the difference between a style that holds and one that collapses by lunchtime.

If you are still deciding, the FAQ page answers the comparison questions directly, and every model in the range is listed under hair dryers with current pricing and colourways.

Airflow, wattage and motor figures are Dyson’s published values for each model. Denaturation temperature and internal bubble formation are from Lima et al., “Heat-damaged evaluation of virgin hair”, Journal of Cosmetic Dermatology, 2019;18(6):1885–1892.