What is a mirror demister pad and how does it work?

A demister is a thin adhesive heating film stuck to the back of the mirror glass. It draws roughly 30 to 60 watts depending on its size and warms that area of the glass a few degrees above the dew point, so vapour cannot settle there. It only keeps clear the area it physically covers, which is why the size and placement of the pad matter more than its wattage.

Is an anti-fog mirror worth it in India?

It depends on your city and your ventilation. In Delhi, Bengaluru, Pune or a hill station, where winter showers are hot and rooms are cold, a demister earns its place. In Mumbai or Chennai, where the temperature gap is small for most of the year, you will use it a few weeks in a row and then forget it. If your bathroom has a working exhaust fan and a window, ventilation solves the problem more completely and costs nothing to run.

Does an anti-fog spray work on a bathroom mirror?

Temporarily. Anti-fog sprays and the old shaving foam trick work by lowering the surface tension so water spreads into a thin sheet instead of forming droplets. The glass is still wet, it just does not scatter light. The coating wears off within days and leaves a film that needs cleaning, so it is a short-term fix rather than a solution.

How much does a demister pad cost to run?

Very little. At 50 watts, running for 30 minutes a day for a month uses about 0.75 units of electricity. At typical Indian domestic tariffs that is a few rupees a month. Running cost is not a reason to avoid one.

Bathroom mirror completely fogged with condensation after a hot shower, droplets running down the glass

Why Does My Bathroom Mirror Fog Up, and What Actually Stops It?

Q: Why does my bathroom mirror fog up?

Because the glass is colder than the air touching it. A hot shower fills the room with warm, very humid air. Tiles and walls have mass and warm up slowly, but mirror glass has almost none and stays near the starting room temperature, so moisture in the air condenses on it as thousands of tiny droplets. Those droplets scatter light, which is what you see as fog.

September 29, 2026

Every winter we get the same message: the mirror fogs the moment the shower goes on, and is there something wrong with it.

There is nothing wrong with it. The mirror fogs because it is the coldest thing in the room, and the fix depends on which of three problems you actually have.

What is happening

A hot shower fills a small room with warm air carrying a lot of water vapour. Air can only hold so much, and how much depends on its temperature. Cool that air down and the water has to go somewhere.

Every surface in the bathroom is a candidate, but the mirror wins. Tiles and plaster have mass, so they slowly warm along with the room. A sheet of glass hanging on a wall has almost none, and its back face is sitting against cool air. It stays close to the temperature the room started at while everything around it heats up.

So the vapour condenses on the glass as thousands of microscopic droplets. Each one bends light a slightly different way. That scattering is the fog. The mirror is still a perfectly good mirror underneath.

Fix one: move the air out

This is the real answer, and the least glamorous.

Ventilation removes the moisture from the room rather than managing one surface within it. A properly sized exhaust fan, run during the shower and for fifteen to twenty minutes afterwards, clears the mirror, and also protects the things you cannot see fogging: the back of the cabinet, the underside of shelves, the ceiling.

Ceiling-mounted bathroom exhaust fan with condensation beading on the tiles around it — Look at the beading on the tiles around this fan. That is the moisture the fan has not managed to pull out yet, and it is the same moisture that lands on your mirror.

Most people switch the fan off with the light, which is exactly when it is needed most. If you are wiring a bathroom, put the fan on a timer that runs on after the light goes off. It is a small part costing very little and it does more for a bathroom than most things you can buy for it.

Fix two: warm the glass

A demister is a thin adhesive heating film stuck to the back of the mirror. Wired so it comes on with the light, it lifts that patch of glass a few degrees above the dew point, and vapour cannot settle on a surface warmer than the air.

Back of a bathroom mirror on a workbench showing the thin silver demister heating pad and its wires — This is the whole thing. A foil pad, an adhesive back and two wires. Notice how much of the mirror it does not cover, which is the part worth understanding before you buy one.

Two things follow from that photograph.

The first is that a demister only clears the area it physically covers. A pad placed centrally on a wide mirror leaves the outer thirds fogged. If you are ordering a mirror with anti-fog, ask where the pad sits and how big it is, not just whether it is included.

The second is that running cost is a non-issue. These draw somewhere around 30 to 60 watts. Half an hour a day for a month is under a unit of electricity, which is a few rupees. Nobody has ever regretted a demister because of the bill.

Fogged bathroom mirror with a clear demisted area kept fog-free by an anti-fog heating pad — The result, honestly photographed. The heated area stays clear and the rest of the glass does not.

Fix three: the ones that do not really work

Anti-fog sprays and the old shaving foam trick both do the same thing. They lower the surface tension so the water spreads into an even film instead of beading up. The glass is still wet. It just stops scattering light.

That is genuinely clever and it genuinely works, for a few days. Then the coating wears off, and in the meantime you have a film on the glass that needs cleaning. Fine before guests arrive. Not a solution.

Leaving the door ajar helps a little by letting moisture escape into a larger volume of air. It also lets the cold in, which in a Delhi January you will not tolerate for long.

So which do you need?

Work through it in this order.

Is there an exhaust fan, and does it actually pull? Hold a sheet of paper to the grille. If it does not hold itself up, the fan is not doing its job and no amount of anti-fog will compensate.
Does it run on after you leave? If not, that is the cheapest upgrade available to you.
Is there still a problem? Now a demister is worth having, and you know to check its size and position.

Geography matters more than people expect. In Delhi, Bengaluru, Pune or anywhere in the hills, the gap between a hot shower and a cold room is wide for months of the year, and a demister gets used daily. In Mumbai or Chennai the gap is narrow for most of the year and the pad sits idle.

The mirror is the part you can see

Everything we have described is happening to every surface in the room. The mirror just reports it. Two other places the same damp causes trouble, both of which people notice late.

The toothbrush. A brush standing in a humid bathroom never fully dries between uses, and bristles that stay damp are where bacteria multiply. Our UV toothbrush steriliser runs a UV-C cycle when you close the lid and then dries at 50 degrees for ninety minutes. The drying is the part that matters, and it is the part most sterilisers leave out. ₹5,200.

Shaving at a fogged mirror. If the main mirror fogs and you shave anyway, a small magnifying mirror on an extending arm is the practical workaround. It is a fraction of the area, so one wipe clears it, and it swings away from the shower when you are done. Ours start at ₹3,199 for a 3X chrome mirror, or ₹7,199 for a version with its own LED ring, which also means you are not depending on the main mirror's light.

What we do

We fit demister pads as an option rather than as standard, and we will tell you when we think you do not need one. A mirror that fogs in a bathroom with no extraction is not really a mirror problem, and selling you a heating pad to paper over it would be the easy answer rather than the right one.

If you want one, we size the pad to the mirror rather than fitting one standard pad to everything, and we will tell you where it sits.

See our bathroom mirrors · See the shaving mirrors

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