Tests 12 Ways To Insulate A Window On The Same Cold Night, Only 3 Were Worth It, And The Shiny Emergency Blanket Everyone Swears By Landed Near The Bottom

Put your hand flat on a window glass in the dead of winter and you already know the problem. A veteran prepper who goes by Ivan decided to find out which cheap fixes actually work, and which ones just look clever on the internet.

A close-up of a frosty window on a cold winter night

In his window insulation test, he lined up 12 different ways to insulate a window along one wall of his house. Same cold exposure, same night, a cheap infrared thermometer from the hardware store, a candle flame to find drafts, and the back of his own hand.

His verdict: only 3 were worth the trouble. And the shiny emergency blanket that half the prepper world swears by landed near the bottom.

Your Window Is “The Hole In Your Bucket,” And It Costs More Than You Think

Ivan says he has lived through three outages that stretched past a couple of days, and each time the window was the weak spot. Warm room air touches cold glass, chills, gets heavy and slides to the floor, while fresh warm air moves in to take its place all night long.

Windows make up only about a tenth of a typical home’s outside surface. But in winter, he says, they can be responsible for something like 30 to 40% of the heat you lose. When the power is on, you see that on the heating bill. When it is off, you feel it on your ankles.

His whole approach comes down to one idea: trap a layer of still air against the glass. Think of a puffy winter coat. It is not the nylon that keeps you warm, it is the air trapped between the feathers.

The second rule is the one most people miss. Moving air beats insulation every time, so a thick blanket over a leaky window accomplishes almost nothing.

Foil, Towels And Even The Emergency Blanket All Failed The Cold Night Test

The bare window was his control, and it grew frost in the corners by morning. The rolled-up towel on the sill, a trick many grandmothers swear by, stopped a little draft but left the glass just as cold. The towel also got damp from condensation and started to smell.

Aluminum foil taped to the glass was a bust too. Foil only works as a reflector when there is an air gap in front of it. Pressed flat against cold glass, Ivan says, it is not a mirror, it is a bridge for the cold, and you give up your daylight to get almost nothing back.

That brings us to the emergency blanket. Ivan keeps a few in his own bags, but taped flat to the pane it did about what the foil did, since the cold passes right through. He says it is a reflector, not insulation, and it earns its keep wrapped around a real blanket or bouncing warmth from a safe heat source, not stuck on a window.

Cardboard did slightly better thanks to the air in its channels, but it soaks up moisture and gets moldy. A bed sheet let air move right through the weave. Ordinary blackout curtains hung a few inches from the wall, open at the top, sides and bottom, so warm air slipped behind them and poured out underneath.

Even real thermal curtains on the same rod had the same gap problem. The surprise loser was rope caulk. It stopped the drafts, and a candle flame stood straight, but the glass stayed exactly as cold as before.

Then Three Cheap Winners Turned The Worst Window On The Wall Into One Of The Best

The first winner was a heat shrink window kit, a sheet of clear film and double-sided tape for under $10 a window. Here is where people go wrong, Ivan says: the tape goes on the frame, not the glass. You stretch the film across the opening, then run a hair dryer slowly over it until it pulls tight as a drum.

What you have built is an extra pane with a pocket of still air. On his wall, the inside face of the plastic read noticeably warmer than the bare glass next to it, the draft disappeared and the frost stopped forming. He calls it a cheap second window, not magic.

The second winner costs even less and may be free. Big-bubble bubble wrap, cut to the size of the glass, goes on after you mist the pane with a spray bottle of plain water. Press it on with the bubbles facing the glass and the water holds it in place. Do not pop the bubbles, because each one is a tiny sealed pocket of still air.

Ivan says estimates he trusts show a layer of bubble wrap can roughly double a single-pane window’s insulating value, though he stresses that is an estimate and the gain is smaller on good double-pane glass. It still lets in soft daylight, and it comes down in seconds. His tip is to write on the corner of each piece which window it belongs to.

The third winner is rigid foam board, the stiff sheets from the building aisle. A 1-inch foil-faced board runs about $10 to $15 and one sheet covers a few windows. Cut it to fit snug in the window opening and add foam weather strip tape around the edges so warm, moist indoor air cannot sneak around it and turn to water on the cold glass.

“Stop The Leaks First” Is The Twist That Made All Three Winners Work

Remember the rope caulk that lost? Ivan says it is the reason the winners work. All three methods trap still air, and if cold air leaks in around the sash, that air is not still anymore. So before any winter covering goes up, he presses rope caulk into the cracks or adds weather stripping where the window meets the frame.

His rule for outages is to pick one warm room, ideally one with few windows and an inside wall, and put your best window work there. South-facing windows are free heaters on a sunny day, so the foam comes out in the morning and goes back in at dusk. Shrink film needs a hair dryer, so it goes up in the fall while the power is still on.

The One Safety Rule He Refuses To Skip

Every room where someone sleeps must keep at least one window that can be opened and climbed out of in seconds, in the dark and in smoke. A foam insert wedged tight into a bedroom window turns a fire escape into a wall.

Ivan notes that rigid foam is a petroleum product that burns, so it stays away from candles, lanterns and heaters. In bedrooms, he says to use bubble wrap or film, which you can tear or push through. Save the foam for living rooms and windows nobody needs as a way out.

Sealing up a room also traps whatever you burn inside it. He is blunt that a grill, camp stove, generator or gas oven never belongs indoors for heat, because carbon monoxide has no smell and no color. Run generators and grills outside, well away from doors and windows, and keep a battery-powered carbon monoxide alarm near where everyone sleeps.

Who Benefits Most, And What To Expect

These fixes shine on old single-pane windows, aluminum sliders that sweat all winter, campers, and winter blackouts. They are also a good fit for renters, since shrink film and bubble wrap come off clean in the spring with no holes and no lost deposit.

The limits are real. None of these heat a house, they only slow the loss of heat you already have. They blur or block your view, and they are not a substitute for storm windows or replacement if you plan to live with drafty glass for years.

A little upkeep helps. Once a week in winter, lift a corner of the bubble wrap or pull a foam insert and look at the glass. Water pooling, mildew or frost means the seal leaks and needs fixing before something rots.

Willow and Hearth