Single glazed windows in a rented flat: does shrink film actually do anything, or is it just theatre?

All three do something, and they do different things, which is why the reviews contradict each other — people are solving different problems and reporting on the same product.

The useful way to separate them is that a window loses heat two ways, and they are independent:

Draught is air physically moving through gaps around the frame and sash. This is the one you feel as a cold stream at ankle height, and it is usually the bigger share in an old wooden window.

Conduction and radiation is heat crossing the glass itself with no air moving at all. This is the one that makes the pane cold to the back of your hand and makes the room feel cold even when there is no draught.

Now the three options sort themselves out:

• Shrink film seals the frame and traps a still air gap against the glass, so it works on both. Trapped still air is a genuinely good insulator — that is the entire principle double glazing runs on, and the film is a cheap version of the same trick.
• A removable secondary pane is the same idea with a bigger, more stable gap and a rigid surface. Better, more expensive, more effort, and it survives being opened.
• Heavy curtains do very little for the glass and quite a lot for radiant comfort, if and only if they seal at the top. An open-topped curtain sets up a convection loop that pulls room air down the cold glass and out at the bottom, which can leave you feeling worse while the meter reads the same.

So film is not theatre. The reviews split because installation is the whole game, not the product.

Renter's practical answer, having done exactly this in two flats.

Start with the draught, because it is free to test and it is usually most of what you are feeling. On a cold day run the back of a damp hand slowly around the frame, the sash join and the bottom rail. You will find the gaps immediately, and often the worst one is not the window at all but the gap under the door to the hall.

Self-adhesive foam or brush strip on the sash costs very little, comes off cleanly if you buy the removable kind, and in an old wooden window it can be the biggest single improvement per pound. Do that first and see what is left.

The other cheap thing nobody mentions: if there is a radiator under that window, make sure the curtain does not hang over it. That arrangement sends a good share of the heat straight up the coldest surface in the room and out. Tucking the curtain onto the sill is free and takes five seconds.

And keep every receipt and every original fitting. Reversibility is the actual constraint in a rental — a fix that improves the room and costs you the deposit is not a fix.

On the condensation, because it is not a side issue and it will decide whether the film is a good idea.

Water appears on the glass because that surface is the coldest thing in the room and the air touching it cools below the point where it can hold what it is carrying. Two variables, and you can attack either: how cold the surface is, and how much moisture is in the room air.

Insulating the glass raises the surface temperature, which genuinely reduces it. But if the room is producing a lot of moisture, all you have done is move the coldest surface somewhere else — the reveal, the corner of the ceiling, the outside wall behind the wardrobe. Those places do not get wiped every morning, which is how a visible condensation problem becomes an invisible one.

So it is worth knowing where the moisture is coming from before sealing anything. In a flat it is usually drying laundry indoors, showers without an extractor that actually reaches outside, and cooking without a lid. Those are all much bigger sources than people assume, and the first one is enormous.

The combination that works is insulate and ventilate, and they sound contradictory but are not: you want less heat leaving and less moisture staying. Short sharp airing beats leaving something ajar all day, because you are trying to swap the air without cooling the walls.

Four winters of film, same three windows, and the difference between "amazing" and "fell off in a week" is almost entirely the tape and the surface under it.

What actually matters:

Clean the frame properly and let it dry. Not a wipe — the tape is fighting years of grease and dust, and it will let go in exactly the spot you skipped. This is the single biggest cause of the one-week failures.

Old paint is the real enemy. On flaking or chalky paint the tape takes the paint off rather than sticking to it, which fails and damages the frame at the same time — the worst of both, and worth knowing before you start in a rented flat. Test a short piece somewhere hidden and pull it off before you commit to a whole window.

Tension it with heat, patiently. The film goes on loose and deliberately baggy, and a hairdryer shrinks it flat. People stop too early because it looks fine, and a slightly slack film flutters, which is what makes it read as cling wrap. Taut, it is close to invisible and you stop noticing it by December.

Leave a small unsealed gap if the window shows heavy condensation. Fully sealing a window that was already streaming can move the moisture problem behind the film where you cannot wipe it, and then you are growing something on the frame instead.

Cost is genuinely small — a kit does a couple of windows and lasts one season. The honest limitation: you have sealed the window shut until spring. In a bedroom you actually ventilate, that is a real trade rather than a detail.