Stop Windows Fogging in Winter with Washing-up Liquid or Glycerine

A simple household staple can put a stop to it.

Plenty of people, still half-asleep, wipe damp windows dry or throw the window open while shivering. Both are irritating, take time, and do nothing for the mood at breakfast. Yet there’s a straightforward trick that older generations used as a matter of course: an everyday product from the cleaning cupboard can sit on the glass like an invisible protective film - and make condensation far less of a nuisance.

Why windows mist up so badly in winter

When it’s cold outside and the heating is on indoors, a familiar bit of physics kicks in. Warm, moisture-laden indoor air hits the cold windowpane. The glass cools the air right at the surface, so it can no longer hold as much water vapour, and the excess moisture settles on the pane as fine droplets. The well-known “dew point” has been reached.

What looks like harmless fogging can cause very real problems:

• Droplets run downwards and dampen window frames and joints.
• Mould spores can take hold on silicone and rubber seals.
• Timber frames swell, and damage can develop over time.
• The air feels clammy, which leads some people to turn the heating up even more.

"If you dry the windows every morning, you’re only tackling the symptom, not the cause: water will keep coming back as long as the surface behaves like a magnet for moisture."

So the solution needs to start at the glass surface itself. The aim is to stop moisture forming dense droplets; instead, the water should spread so thinly that it’s barely visible - or not cling to the glass in the first place.

The simple trick: washing-up liquid or glycerine as a protective film

This is where a practical everyday method comes in - one that divers, skiers, and motorcyclists have relied on for years. They apply a thin film of washing-up liquid or glycerine to masks, goggles, or visors to prevent fogging. The same approach works just as well on windows.

Both substances act as surfactants. They lower surface tension and change how water behaves on glass.

"Instead of lots of tiny droplets creating a milky haze, the moisture becomes an ultra-thin, almost invisible film - light still passes through, and the view outside stays clear."

For day-to-day use, two options are especially practical because most households already have one of them:

• Glycerine (vegetable or pharmaceutical grade) - available from pharmacies and chemists, and a little goes a long way
• Clear washing-up liquid - one small drop is enough, ideal for large window areas

Both create a water-repelling or water-spreading effect. Moisture either beads off or lies flat, rather than forming small globules that cloud the pane.

Step by step: how to treat your windows properly

To get the benefit without leaving the glass looking greasy, preparation and dosage matter. The process is similar to a thorough clean, but it only takes a few minutes.

1. Clean the window thoroughly

Before applying the anti-fog film, the pane should be clean and dry. Otherwise, dust, grease, or fingerprints get sealed under the layer and can later show up as streaks.

• Clean the window as usual using glass cleaner or a vinegar-and-water solution.
• Dry with a lint-free cloth or a squeegee.
• Use a dry cloth to pick up any residue around the edges.

2. Use a tiny amount of product

At this stage, less really is more. Using too much is the quickest way to end up with smears.

• Put one drop of washing-up liquid or glycerine onto a slightly damp microfibre cloth.
• Rub it into the cloth a little so there isn’t a wet patch.

If you’re dealing with large panes or glazed doors, refresh the drop gradually as needed - but don’t drip it straight onto the glass.

3. Rub in and polish

Now you apply the “protective coating”:

• Wipe the entire inside surface using circular movements.
• It’s better to go over the same area a few extra times than to apply a thick layer.
• Then buff with a second, dry, soft cloth until the glass looks clear again.

"Important: don’t wipe over with water afterwards. The barely visible residue is exactly what acts as the anti-fog film."

If you can see rainbow-like streaks or a greasy sheen, you’ve used too much. Polish firmly again with a dry cloth - in most cases the haze will disappear.

How long does the effect last - and where does it work best?

If you treat the glass in the evening, you’ll usually notice the difference the very next frosty morning: treated windows stay clear, while untreated sections visibly mist up. In many homes the effect lasts several days, and in drier rooms it can hold for up to a week.

This method is particularly useful in typical trouble spots:

• bedroom windows, where a lot of moisture builds up overnight
• bathroom windows if there isn’t continuous extraction
• kitchen windows near the hob
• balcony or patio doors in the living room

If humidity is extremely high - for example, after a long shower without airing - some moisture may still settle even with the protective film, but it will be noticeably reduced. Regular rapid airing is therefore still worthwhile.

More than clear glass: protection for frames and the indoor climate

This trick doesn’t just preserve the view; it also helps protect the building fabric. When less water runs down the pane, frames and joints stay drier, reducing the risk of damp marks and mould along the seals.

"Every puddle avoided on the window sill means less moisture in the nooks where fungi particularly like to thrive."

Many people also describe the room as feeling more comfortable. The sense of a “cold wall” created by wet glass fades. If the room subjectively feels less chilly and draughty, people are less likely to instinctively crank up the thermostat - which can save on heating costs over time.

How to combine the trick with other measures

The anti-fog film doesn’t replace the basic rules for keeping indoor humidity under control, but it complements them well. Useful combinations include:

• Rapid airing instead of leaving windows on the latch: Cross-ventilate several times a day for five to ten minutes.
• Limit sources of moisture: Avoid drying laundry in living spaces where possible; use lids when cooking.
• Keep an eye on temperature: Don’t let rooms cool down completely; it helps prevent big temperature differences.
• Check houseplants: Lots of large indoor plants can noticeably raise humidity.

In some older properties with very thin panes and poor insulation, even expensive electric dehumidifiers reach their limits. In those cases, the simple film made from washing-up liquid or glycerine can be surprisingly dependable - especially during the coldest months.

When the trick is less suitable - and what to bear in mind

There are times when a more cautious approach makes sense. If you’re sensitive to fragrances, choose a neutral, unperfumed washing-up liquid, or use glycerine instead. Glycerine is odourless and comes in small bottles that last a long time.

If your glass has specialist high-tech coatings - such as self-cleaning panes or heavily mirrored finishes - it’s sensible to check the manufacturer’s guidance first. Some explicitly advise against adding any extra layer. With standard double-glazed household windows, this is not usually an issue.

If you have pets that like to lick windows, or children who constantly touch the glass, you may need to re-polish a bit more often. The protective film remains effective, but it can wear away faster in heavily used areas.

An old trick that makes winter life noticeably easier

Whether it’s a rented flat in an older building or a house with large glazed areas, condensation on windows is one of the most common winter annoyances. Washing-up liquid or glycerine shows how much can be improved with the simplest means: no specialist spray, no electricity use, no high price - just a drop, a little time, and a microfibre cloth.

Once you’ve got the routine down, it’s easy to fold into normal cleaning. On days when overnight frost is forecast, a quick extra pass in the evening is particularly worthwhile. The next morning, instead of wet cloths and fogged-up panes, you get a clear view of winter.