On a hot summer afternoon, a south or west-facing room with unprotected windows becomes an oven. Solar energy streaming through glass heats surfaces, floors, and furniture, which then re-radiate heat into the air - a process that can push room temperature 10-15 degrees above the thermostat set point. The fastest and cheapest way to address this is at the window, before the heat enters the room.
These five curtains use different heat-blocking mechanisms - solar shade screening, reflective backings, and thermal foam cores - to intercept summer heat at the source.
| Panel | Mechanism | Heat Reduction | Best Window |
|---|---|---|---|
| Coolaroo Indoor Sun Shade | Knitted solar screen | Very high | South / west facing |
| Eclipse Suede Thermaback | Foam thermaback | High | Bedroom |
| HOMEDEX Sun Blocking Thermal | Reflective thermal | High | Living rooms |
| Insola Thermaback Energy | Energy-rated foam | High | Any exposure |
| Rideaux White Reflective Blackout | White reflective | Highest | Direct sun |
1. Coolaroo Indoor Sun Shade
Coolaroo’s knitted polyethylene shade fabric was originally developed for outdoor use in extreme climates and adapted for interior window application. The open-knit construction blocks solar radiation before it penetrates the glass zone while allowing air circulation - making it uniquely effective in rooms where total blackout is not desirable but solar heat gain is the primary problem.
Pros: Screen-based solar blocking that addresses heat at the glass surface, maintains partial view and airflow unlike blackout panels, UV rating certified rather than estimated, cooler and lighter than heavy drape alternatives.
Cons: Not a traditional curtain - requires separate mounting track or rod, functional appearance does not suit all decor styles, provides minimal privacy at night when interior is lit.
2. Eclipse Suede Thermaback Curtain
Eclipse’s suede thermaback line applies a foam thermal lining to a suede-textured face fabric - the result is a curtain that looks upscale while providing foam-core heat and light blocking. The thermaback foam layer creates an air gap between the glass and the room, which significantly reduces conductive and radiant heat transfer.
Pros: Foam thermaback provides genuine thermal resistance, suede face fabric elevates room aesthetics above standard blackout panels, good blackout performance alongside heat blocking, grommet heading makes installation easy.
Cons: Suede texture shows dust and lint more than smooth fabrics, foam core can degrade after prolonged UV exposure (keep curtains closed to protect the backing), dry clean recommended for many suede-face panels.
3. HOMEDEX Sun Blocking Thermal Curtain
HOMEDEX’s sun blocking thermal panels use a dense microfiber construction with an integrated reflective layer to address heat blocking from two angles: absorption resistance in the face fabric and solar reflection from the backing. These panels are particularly effective in living rooms where you want room-darkening rather than full blackout alongside heat reduction.
Pros: Dual-mechanism heat blocking (absorption and reflection), room-darkening rather than total blackout preserves some natural light, wide colour range in neutrals and earthy tones, machine washable, affordable price point.
Cons: Room-darkening rather than full blackout means some light transmission remains, reflective backing is not visible when hung but must face the window to be effective, lighter weight than pure blackout alternatives.
4. Insola Thermaback Energy Curtain
Insola’s thermaback energy line carries an independent energy efficiency certification - meaning the thermal performance claims have been verified rather than self-reported. These panels use a proprietary foam backing rated for meaningful heat gain reduction, and the certification is particularly useful for renters or homeowners who want documented performance for energy rebate programs.
Pros: Verified energy performance rather than marketing estimates, foam backing provides consistent thermal resistance, wide size range covers most residential windows, practical neutral colour options that suit transitional decor.
Cons: Certification adds a slight premium to the price, foam backing degrades over time (typically 5-8 years), functional aesthetic is more about performance than design statement.
5. Rideaux White Reflective Blackout Curtain
White or silver reflective backings on blackout panels are the most thermally effective residential window treatment available outside of exterior shutters. The white face reflects light aesthetically while the reflective backing deflects solar infrared radiation away from the room before it can be absorbed by interior surfaces. For rooms with intense afternoon west-facing sun exposure, this is the maximum-performance solution.
Pros: Highest heat-blocking performance of any fabric curtain type, white face keeps rooms looking bright and intentional, reflective backing works on both infrared and visible light, extremely effective on direct-sun windows.
Cons: Limited to white or very light face colours due to the reflective backing system, exterior appearance can be stark (bright white visible from outside), must ensure the reflective side faces the glass to function correctly.
What to Look For
Reflective backing: For summer heat blocking specifically, a white, silver, or metallised backing on any curtain type will outperform dark-coloured panels of equivalent construction. The backing faces the window and reflects solar infrared before it enters the room.
Window orientation: West-facing windows receive the most intense afternoon heat in summer. South-facing windows get sustained sun exposure throughout the day. Prioritise these exposures - east and north-facing windows rarely need heat-blocking treatment in most climates.
Overlap and mounting: Heat-blocking panels need to cover the entire glass area with minimal gaps. Use a rod that extends 6 inches past each side of the window and keep panels closed during peak sun hours (10am-4pm) for maximum effect.
Final Thoughts
The highest-impact heat-blocking upgrades are on your west and south-facing windows during afternoon hours. Start with the Rideaux white reflective blackout panel on your hottest exposure - the reflective mechanism provides better results than any dark-coloured panel regardless of thickness. For rooms where you want some daylight, the Coolaroo sun shade or HOMEDEX room-darkening option keeps the heat out while maintaining a liveable light level. Your air conditioner will notice the difference.
Frequently asked questions
How much can curtains reduce room temperature in summer?+
Research from the US Department of Energy shows that medium-coloured drapes with white plastic backings can reduce heat gain through windows by 33%. Reflective or white-backed panels on south and west-facing windows can reduce room temperature by 4-8°F during peak afternoon sun hours, reducing air conditioning load significantly.
Should curtains be open or closed to keep heat out?+
Closed is always better for heat reduction when the sun is directly striking the window. The best approach: close heat-blocking curtains during peak sun hours on south and west-facing windows, then open them in the evening when outside temperature drops below inside temperature to flush cool air through.
Does curtain colour matter for heat blocking?+
Yes. White and light-coloured curtains reflect solar radiation; dark curtains absorb it and re-radiate heat into the room. For maximum heat blocking, choose panels with a white or metallic reflective backing regardless of the face colour. The backing faces the window and does the actual work of deflecting solar energy.