Stopping sunlight at the window is the highest-impact way to keep a room cool, and two popular indoor options compete for the job: blackout curtains and thermal window films. Here's how they compare and which suits your situation.
How each one works
The two attack window heat differently:
- Blackout curtains hang inside the window and block light, absorbing or reflecting some heat after the sun has passed through the glass. Light-coloured or thermally-lined versions perform best.
- Thermal/reflective window films stick to the glass itself and reflect a portion of the sun's energy before it fully enters the room, tackling the heat earlier in its path.
Because film acts at the glass and curtains act behind it, film generally blocks more heat.
Heat blocking: film usually wins
If raw heat reduction is your priority, reflective window film typically blocks more, because stopping sunlight at the glass beats intercepting it after it's already inside. Curtains still help meaningfully — a closed thermal curtain on a sunny window makes a real difference — but they're working a step too late to match a good reflective film.
Convenience and renting: curtains win
For ease and rentals, curtains are the clear choice. They hang on an existing rail, open and close freely, come down when you move, and pose no risk to your deposit. Window films are more permanent, fiddly to apply bubble-free, and adhesive types can be hard to remove cleanly — though removable static-cling films avoid the adhesive problem and are a renter-friendlier middle ground.
The honest comparison
| Blackout curtains | Thermal/reflective film | |
|---|---|---|
| Heat blocked | Good | More |
| Convenience | High (just close them) | Lower (apply once) |
| Renter-friendly | Yes | Cling films yes, adhesive less so |
| Reversible | Fully | Cling yes, adhesive harder |
| Also blocks light | Yes | Varies by film |
Both lose to outdoor shading
Here's the bigger truth: any indoor solution works after sunlight has already entered the glass, while outdoor shading — roller shutters, external blinds, awnings — stops it before it gets in, and blocks far more heat than either curtains or film. If you can shade from outside (it may need landlord permission), do that first, then use curtains or film as a supplement.
How to choose
Renting and want easy, reversible heat blocking? Go with blackout curtains. Want maximum indoor heat reduction and don't mind a one-time application? Reflective film does more. Either way, combine it with night ventilation and, if needed, a fan or cooler to keep the room comfortable. Block the sun first, then cool what's left.