Condensation, Curtains and the Cape Winter — What Actually Helps
The short answer: Condensation forms when warm, moist indoor air touches cold glass and cools past its dew point, leaving water on the window — and Cape Town’s cool, wet, humid winters from June to August are prime conditions for it. Curtains do not create condensation; the real drivers are indoor humidity and ventilation, and a curtain changes neither. A well-fitted thermal curtain can even reduce condensation on the glass slightly by buffering the temperature, but fabric absorbs moisture and can grow mould if a room stays damp, so in a very wet room a wipeable blind is often more practical. The things that actually work are ventilation, steady gentle heating, and wiping the glass.
Every Cape winter it starts again: you wake up, pull back the curtains, and the window behind them is running with water. It is easy to blame the curtains — but they are mostly innocent. Condensation is a story about warm air, cold glass and moisture, and understanding it is the difference between wiping a window forever and actually fixing the room.
How condensation actually forms
Warm air holds more moisture than cold air. When the warm, humid air inside a heated room meets a cold windowpane, the air right at the glass cools until it reaches its dew point — the temperature at which it can no longer hold all that moisture — and the water comes out as droplets on the glass. It is worst in winter for the obvious reason: the outside cold makes the glass cold, while the room stays warm and damp.
Why the Cape winter is condensation season
Cape Town has a Mediterranean climate — dry summers and mild, wet winters. The rain concentrates from about May to August, with roughly 70 to 85 mm falling each of those months across nine or ten rainy days, and winter humidity sitting around 76 to 77 per cent. Add nights that drop toward 7 °C and homes that are heated in the evening and cool by morning, and you have exactly the warm-inside, cold-glass, humid-air combination that leaves windows streaming.
Do curtains cause condensation?
No. Curtains neither add moisture to a room nor change its ventilation, and those two things — humidity and airflow — are what actually govern condensation. If anything, a thick, well-fitted thermal curtain can reduce condensation on the glass a little, because the pocket of air it traps softens the temperature difference across the window. The curtain is not the villain; the damp, still air in the room is.
The real risk: damp and mould in the fabric
Where curtains do get into trouble is by absorbing the moisture around them. Fabric hanging in a persistently humid room will eventually get damp, start to smell musty, and can grow mould or mildew — especially behind a curtain that stays closed over a cold, wet window where the air barely moves. That is a fabric-care problem rather than a condensation cause, but it is the reason curtains in a chronically damp room need airing, washing, and a room that dries out between wettings.
Curtains or blinds for a damp room?
Neither curtains nor blinds will cure condensation, because neither lowers humidity or adds ventilation. But in a room that condenses heavily every winter, a wipeable blind has a practical edge: a waterproof or moisture-resistant blind can be dried off with a cloth and will not soak up moisture the way fabric does. It is why bathrooms and kitchens — the dampest rooms in the house — so often suit blinds or shutters rather than full curtains.
What actually helps
The fixes all target moisture and airflow, not the window covering. Ventilate — open a window or run an extractor fan when you shower, bathe or cook, and try to dry washing outside rather than on an indoor rack. Heat gently and steadily — keeping a low, constant warmth stops the glass getting cold enough to condense in the first place. Wipe the glass — clearing the morning water with a cloth or a window vacuum stops it soaking into sills and frames. And deal with it quickly, because damp left sitting on a surface for more than about a day is what lets mould take hold.
Frequently asked questions
Do closed curtains cause condensation?
No. Curtains do not add moisture or change a room’s ventilation, which are the two things that drive condensation. A well-fitted thermal curtain can even reduce condensation on the glass slightly by buffering the temperature.
Why is my window wet on winter mornings in Cape Town?
Overnight the glass cools while the room stays warm and humid, so the moist indoor air condenses on the cold pane. Cape Town’s winters are both wet and humid, which makes it especially common from about May to August.
Can curtains go mouldy from condensation?
Yes. Fabric in a persistently humid room absorbs moisture and can start to smell damp or grow mould and mildew, particularly behind a closed curtain over a cold, wet window where the air is still.
Are blinds better than curtains for condensation?
Neither cures it, because neither lowers humidity. But a waterproof or wipeable blind copes better in a very damp room, since it can be dried with a cloth and does not soak up moisture like fabric.
Do thermal or blockout curtains make condensation worse?
No. A thick, well-fitted thermal curtain tends to reduce condensation on the glass a little, because the trapped pocket of air softens the temperature difference across the window.
What actually stops window condensation?
Ventilation and moisture control: open windows or extractor fans when cooking or washing, dry laundry outside, keep a low steady warmth so the glass is not freezing, and wipe the window each morning.
How quickly can mould form from condensation?
Damp left sitting on a surface for more than about 24 hours is enough for mould and mildew to begin growing, which is why wiping condensation away promptly matters.