Thermal & Energy

Blinds to keep heat out

It is 4 pm in February. The aircon has been running since lunch. The room still feels like a sauna.

The reason is simple, and it is not your aircon’s fault. The sun has been pouring through your west-facing windows for hours, and every degree of that heat has been absorbed by your floors, your walls, and your couch. You are not cooling a hot room. You are cooling a room with the heat already loaded into the surfaces.

The fix is to stop the sun reaching the inside of the glass in the first place. Done right, the room never gets that hot, and the aircon never has to fight a backlog.

Here is how blinds keep the heat out, why most blinds do not, and what to look for if you want a real fix.

Why summer heat hits Australian rooms so hard

The biggest source of indoor heat in summer is solar gain, sunlight passing through glass, landing on a surface, and converting to heat. A single-pane window with direct afternoon sun on it is effectively a small radiator pointed at your living room.

Three things make it worse in Australian homes:

Orientation. West-facing rooms get the worst of it from 2 pm onward. North-facing rooms cop the late morning. South is usually fine.
Single-pane glass. Older homes especially. Almost no resistance to radiant heat.
Large glazing. Floor-to-ceiling windows, sliding glass doors, picture windows. The bigger the glass, the bigger the radiator.

If you have any combination of those three, your aircon is fighting a losing battle from lunchtime.

How blinds actually keep heat out

A blind that genuinely blocks heat does three things at once.

Reflects solar energy back outward. A blockout fabric with a reflective white back bounces a large portion of the incoming sunlight back through the glass before it lands inside the room. This is the biggest win. Heat that never enters the room never has to be cooled.
Absorbs and disperses what gets through. A foam-backed fabric soaks up residual heat in the layer between the surface and the room. Heat that gets past the reflection is held in the fabric, not radiated onto your couch.
Seals the gap. Side channels and brush seals stop hot air leaking around the edges of the blind. Without the seal, warm air rolls past the blind and circulates inside the room anyway, defeating the point.

The third one is the one most people miss. A standard roller blackout blind without side channels still lets heat in around the sides. The fabric is doing its job. The gaps are not.

Do blackout blinds keep heat out?

Yes, when they have all three components above. A blackout fabric on its own blocks the light but leaks heat around the edges. A blackout fabric with side channels and seals creates a sealed barrier that reflects, absorbs, and prevents air bypass. The whole package matters.

This is also why curtains alone struggle in summer. They block light, but air flows freely around the top, the sides, and underneath. The room still heats up, it just heats up in dimmer light.

What is the best blind to keep heat out?

In the Australian market, two formats actually block solar heat. The trade-offs are different for each.

Sunscreen blinds. Mesh fabric that filters sunlight. They preserve the view and reduce glare while cutting some of the solar load. A 5% openness sunscreen blocks roughly 90% of solar radiation, which sounds great until you realise the missing 10% is still significant on a 35-degree day. They do not insulate (no still-air pocket), and they do not block 100% of the heat.

Sealed blockout blinds. Foam-backed blockout fabric in a cassette with aluminium side channels and brush seals top and bottom. Reflects effectively all visible light, blocks effectively all radiant heat, and creates a still-air insulating pocket against the glass. Trade-off: when you drop them, the room is dark. So you only run them when the sun is on the glass.

The clearest answer for most homes: sunscreens on the windows you want to watch through during the day, sealed blockout blinds on the windows that bake your living room. Different tools, different jobs. The mistake is using sunscreens everywhere and wondering why the lounge is still 30 degrees at 4 pm.

Which windows to prioritise

If you are buying a few at a time, hit these in this order:

West-facing main living rooms. Worst solar gain, biggest comfort impact. Start here.
Bedrooms that do not cool overnight. Especially north or west-facing. Cool sleep is non-negotiable.
North-facing rooms with large glazing. The late-morning load creeps up on you.
Sliding glass doors and picture windows. Big surface area, big problem.

Bathrooms and laundries are low priority, small windows, low occupancy. Kitchens are mid-priority unless you have a west-facing window over the sink.

How much aircon can you actually save?

Real expectations, not marketing claims:

The aircon turns on later in the afternoon, because the room takes longer to load up with heat.
The aircon switches off sooner, because there is less heat to remove.
The aircon runs at lower duty cycles overall, instead of flat-out for hours.
Bedrooms cool down faster at night because the walls and floors are not radiating accumulated heat back into the room.

The biggest gain is on west-facing living rooms with single-pane glass. The smallest gain is on south-facing rooms with double glazing already (those rooms were not the problem to begin with). Most homes get a noticeable difference on the first hot afternoon after install.

You can install them yourself

Every Coverlight thermal blackout blind ships ready to install without a tradesperson. Measure the window using our DIY measuring guide. Order online. Two screws each side, the blind clicks into the brackets, the side channels seal it shut. Our installation guide covers the whole process, most rooms take 15 to 20 minutes.

No installer means no booking three weeks out, no $400+ install fee per opening, and no waiting for the next heatwave to feel the difference.

Stop paying to cool a sun-loaded room

You do not need to keep cooling a room that the sun keeps reheating. A sealed blockout blind on the windows that hit hardest will lift the floor of your living room comfort and drop the ceiling of your power bill at the same time.

Shop heat blocking blinds and save up to 20% →