A south or west-facing room can climb several degrees above the rest of the house on a clear summer day, and the cause is almost always the windows. Glass lets sunlight in freely, that light lands on floors, walls and furniture and turns to heat, and the heat is then trapped inside because it cannot pass back out through the glass as easily as the light came in. That is the greenhouse effect working against you in your own living room. A blind cannot stop the sun, but the right one intercepts a good share of that incoming light before it becomes trapped heat. This guide explains how, and compares ten picks for keeping a room cool.
How a blind keeps a room cool
The single most useful idea here is that heat is far easier to keep out than to remove once it is in. Light passes through glass, strikes a surface, and converts to long-wave heat that the glass then holds in. So the job of a cooling blind is to deal with the light at the window, before that conversion happens, rather than to mop up warmth afterwards.
Three things decide how well a blind does that. The first is reflectivity. A pale or metallic surface bounces a large part of the sunlight straight back out through the glass, where a dark surface absorbs it and re-radiates much of it into the room as heat. This is why a white or silver blind runs cooler than a navy one in the same window, and why the colour you choose matters as much for temperature as for looks.
The second is the ability to angle the light. A venetian blind, whether aluminium or wood-effect, tilts its slats so you can throw direct sun up towards the ceiling or down towards the floor and away from where people sit, while still letting some daylight and air through. That control is something a flat fabric cannot offer, and it is why slatted blinds feature strongly in any cooling guide.
The third is insulation. A cellular, or honeycomb, blind traps a layer of still air in its cells, and that buffer slows heat crossing the glass in both directions. In winter it holds warmth in; in summer it slows the sun's heat coming through, particularly useful on a rooflight or a window that catches sun for hours.
One honest limitation runs through all of this. A blind sits on the warm side of the glass, so it cannot match external shading - an awning, a brise-soleil or even a tree stops the light before it ever reaches the window, which is always more effective. An internal blind still helps a great deal, especially a pale or reflective one closed before the sun comes round, but the realistic aim is to take the edge off a hot room, not to air-condition it with fabric.
What to look for
Pale and reflective beats dark. For temperature, lean towards white, cream, silver or light grey. A dark blind looks smart but absorbs the sun and gives much of that heat back to the room.
Slats for control. An aluminium or wood-effect venetian lets you deflect direct sun off the seating area while keeping the room light and ventilated. Aluminium reflects more than wood, so for pure heat control the metal slat leads.
Close it before the heat, not after. A blind works by stopping light landing inside. Drawing it as the sun comes round to that side, rather than once the room is already warm, is the difference between keeping heat out and trying to trap it in.
Cellular for the worst offenders. For a conservatory roof, a rooflight, or a window in sun for most of the day, a honeycomb fabric's trapped-air layer slows the relentless gain in a way a single sheet cannot.
Think about the whole opening. Big patio doors and bay windows gain a lot of heat simply because they are large. Vertical louvres suit wide glazing, angling to cut the sun while keeping the doorway usable.
Pair it with airflow. A blind that blocks sun while a window stays cracked for a through-draught keeps a room far cooler than a sealed, shaded box. Light-filtering fabrics let you shade and ventilate at once.
Our picks
Aluminium Venetian
at So Easy Blinds
Metal slats that tilt to bounce direct sun back out before it heats the room.
Hades Aluminium Venetian
at Make My Blinds
The same reflective slat approach at a lower entry price.
Honeycomb
at 247 Blinds
Honeycomb cells that slow heat passing through the glass either way.
Orion (Blackout)
at 247 Blinds
A dense roller that blocks the sun outright for a room that must stay cool.
Choices Roller
at Blinds 2go
A vast colour run including the pale, reflective tones that shed heat best.
Atlantex Perfect Fit Roller
at So Easy Blinds
A light roller fabric that reflects glare and warmth without full darkness.
Totalshade Complete Blackout Thermal
at Blinds 2go
A blackout-thermal pleated for the glass that gains the most heat.
Spectrum
at 247 Blinds
Tilt-control slats in a warmer wood-effect finish for living spaces.
Orion (Blackout)
at 247 Blinds
Vertical louvres that angle the sun off large areas of glazing.
Bella (Blackout) Blackout Roller
at So Easy Blinds
A broad blackout roller range that blocks heat and suits most rooms.
Pick details
Best reflective
Aluminium Venetian
at So Easy Blinds
Metal slats that tilt to bounce direct sun back out before it heats the room.
For sheer heat control, reflective metal slats lead, and this aluminium venetian is our pick. The slats bounce a large part of the direct sun back out through the glass, and because they tilt you can aim the rest up at the ceiling and away from where you sit while keeping the room bright and airy. The broad colour run includes the pale and silver tones that shed the most heat. It suits a sunny kitchen, bathroom or home office where you want light and ventilation without the room heating up, and where a slatted look fits the space.
Best aluminium value
Hades Aluminium Venetian
at Make My Blinds
The same reflective slat approach at a lower entry price.
For the same reflective-slat approach at a gentler price, this aluminium venetian gives the tilt control and the heat-deflecting metal surface without the broadest palette. The cooling principle is identical - reflect the sun, angle the rest away - so where budget leads and you want the practical benefit rather than the widest choice of finishes, it does the core job well across a sunny window.
Best cellular
Honeycomb
at 247 Blinds
Honeycomb cells that slow heat passing through the glass either way.
For a window that bakes for hours, or a rooflight you cannot easily reach, the honeycomb roller's cells trap a layer of air that slows the heat crossing the glass. It is the pick where insulation matters more than slat control - a room that overheats through sustained gain rather than a single shaft of afternoon sun. The same cells that hold warmth in over winter work the other way in summer, slowing the build-up, which makes it a sensible year-round choice for a hot room.
Best blackout roller
Orion (Blackout)
at 247 Blinds
A dense roller that blocks the sun outright for a room that must stay cool.
Where a room simply has to stay cool and dark, a dense blackout roller blocks the sun outright. Choose it in a pale shade and it reflects from the outward face while excluding light on the inward one, so a bedroom or a media room stays both dark and noticeably cooler through the afternoon. It gives up the airflow and the view that a slatted or light-filtering blind keeps, so it suits the rooms where full shade is the point rather than living spaces you want bright.
Best palette
Choices Roller
at Blinds 2go
A vast colour run including the pale, reflective tones that shed heat best.
When the colour has to be right and you still want it to run cool, this roller range offers an unusually wide run of finishes, including the pale, reflective tones that shed heat best. The breadth means you can match a scheme precisely and still pick a shade that works with the sun rather than against it. A strong choice for a room where appearance leads but you are unwilling to give up the cooling benefit of a light fabric.
Best solar roller
Atlantex Perfect Fit Roller
at So Easy Blinds
A light roller fabric that reflects glare and warmth without full darkness.
For a room you want to keep cool without plunging into darkness, this light roller fabric reflects glare and a share of the warmth while still passing soft daylight. It suits a home office or a living room that catches afternoon sun, where a blackout blind would be too much but bare glass is too hot. You shade and soften the light, cut the heat at the window, and keep the room usable rather than dim.
Best for conservatories
Totalshade Complete Blackout Thermal
at Blinds 2go
A blackout-thermal pleated for the glass that gains the most heat.
A conservatory or a wall of glazing gains more heat than any other part of a house, and here a blackout-thermal pleated earns its place. The dense fabric blocks the sun, and the thermal build slows the heat that does reach it, tackling the worst-case window with both tools at once. Fitted close to the glass in a perfect-fit frame, it suits the panes that turn a garden room into a greenhouse by mid-afternoon.
Best wood-look venetian
Spectrum
at 247 Blinds
Tilt-control slats in a warmer wood-effect finish for living spaces.
For tilt control in a warmer finish than bare metal, this wood-effect venetian angles the sun off the seating area while bringing a softer look to a living room or bedroom. It reflects less than aluminium, so it trades a little outright heat control for appearance, but the slat control is the same - deflect the direct sun, keep the daylight. The pick where a metal slat would feel too utilitarian and you want the cooling benefit with a more domestic finish.
Best for patio doors
Orion (Blackout)
at 247 Blinds
Vertical louvres that angle the sun off large areas of glazing.
Large patio doors and full-height glazing gain heat simply through their size, and vertical louvres suit them. The vanes angle to cut the sun off the room while keeping the doorway walkable, and they draw aside cleanly when you want the garden open. In a dense shade they block a great deal of the gain through a big opening that a single roller would struggle to cover neatly. The pick for wide glazing where coverage and access both matter.
Best all-rounder
Bella (Blackout) Blackout Roller
at So Easy Blinds
A broad blackout roller range that blocks heat and suits most rooms.
For a dependable cooling roller that suits almost any room, this broad blackout range blocks the sun in a wide choice of colours, so you can pick a pale shade that runs cool and still match the space. It is the sensible default where you want real heat control without a slatted or specialist fabric - a clean roller, in the right light tone, drawn before the sun comes round. A safe, flexible starting point for cooling a room.
What we left out
A couple of genuinely cooling options sit outside this guide for honest reasons.
External shading beats any internal blind. An awning, an external louvre or a shade sail stops the sunlight before it ever reaches the glass, which is the most effective approach of all. The reason it is not among the picks is that this is a guide to blinds fitted inside the window, a different and far more common purchase; if you are reworking the outside of the house, external shading is well worth pricing alongside.
Solar-reflective window film also helps, and it pairs well with a blind rather than competing with it. It is left out because it is a glazing treatment rather than a blind, applied to the pane itself, so it belongs to a different decision. Used together, a reflective film and a pale blind shed more heat than either alone, which is the better framing than choosing between them.
Price by your window
The from-prices shown are starting points; the made-to-measure price depends on your window's width and drop, and the larger glazing that gains the most heat naturally costs more to cover. Each pick's page has a price-by-dimensions tool, so enter your measurements for the price at your size. The aluminium venetians and the value roller sit lowest; the cellular and conservatory picks come higher for the insulating structure they carry.