Chloe Zhang
The colour of plastic can have a significant impact on its ability to reflect heat. When sunlight hits an object, some of the visible light is converted to heat. Lighter colours made with reflective materials and short-wavelength-absorbing pigments tend to reflect more light and stay cooler, while darker colours absorb more light across the visible spectrum and heat up more quickly. This principle is applied in various contexts, from choosing clothing that keeps us cool in hot weather to selecting exterior paint colours for buildings to reduce indoor temperatures. Understanding the heat reflectance properties of different colours can help make informed choices to optimise comfort and energy efficiency.
| Characteristics | Values |
|---|---|
| Colour that reflects heat the best | White |
| Colour that reflects IR radiation the best | Dark brown |
| Colour that absorbs heat the most | Black |
| Effect of sheen/finish | Glossy or shiny surfaces reflect more light and heat than matte or textured finishes |
| Effect of colour on cooling | Light colours reflect more light and heat, keeping objects and buildings cooler |
| Effect of colour on heating | Dark colours absorb more light and heat, making them ideal for keeping warm |
| Application in building materials | White roofing and cladding materials are used to keep buildings cooler and reduce the demand for air conditioning |
| Application in clothing | Light-coloured clothing reflects heat and keeps people cooler in hot climates |
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What You'll Learn
White plastic reflects heat
When sunlight hits an object, some of it is converted to heat energy. The colour of the object determines how much heat it absorbs. This is because an object's colour depends on which wavelengths of light it absorbs and which it reflects.
The colour white reflects the most solar heat, keeping surfaces cooler than darker colours. Dark colours absorb more sunlight than lighter ones, which is why wearing black clothing on a hot day can make you feel even hotter. Black absorbs up to 90% of sunlight as heat, making it the hottest colour in sun exposure.
However, it is important to note that the reflectance characteristics of colours can differ in the IR range. While white reflects most visible light, it is unclear whether this outweighs the heat contribution from other wavelengths.
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Dark colours absorb heat
Dark colours absorb more heat from sunlight than lighter colours. This is because darker colours absorb more light across the visible spectrum compared to lighter shades of the same hue. The more light an object absorbs, the more it heats up. Therefore, dark colours absorb more heat and lighter colours reflect more heat.
The colour black absorbs the most heat out of all colours. This is because black absorbs all the light and reflects little to none, converting more heat. Black absorbs up to 90% of sunlight as heat, making it the hottest colour in sun exposure. On the other hand, white objects reflect nearly all visible wavelengths equally, making white the coolest colour.
The heat absorption of colours can be influenced by other factors. For example, longer wavelengths like red and orange are more likely to be absorbed and converted to heat compared to shorter wavelengths like blue and violet. Additionally, glossy or shiny surfaces reflect more light while matte or textured finishes absorb more. For example, a shiny deep blue will still absorb more heat than a shiny yellow.
The application of these principles can be seen in various contexts. In the fashion industry, dark-coloured clothes are marketed during colder months and light-coloured clothes during the summer. This is because light-coloured garments absorb less light, producing less heat and keeping the wearer cooler. Similarly, when choosing paint for a house exterior, lighter colours like white or light yellow are preferable to darker colours like red or brown in order to keep the building cooler.
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Black plastic absorbs heat
When it comes to the colour that reflects heat the best, not all colours are created equal. Some colours absorb more heat from sunlight than others, causing surfaces painted those colours to get hotter. White objects reflect nearly all visible wavelengths equally, while black objects absorb most of the light that hits them. This is because darker colours absorb more sunlight than lighter ones. Black absorbs up to 90% of sunlight as heat, making it the hottest colour in sun exposure.
This phenomenon has many practical implications. For example, in the building industry, white is extensively used due to its reflective properties, but there is a demand for darker colours which are aesthetically more pleasing. However, exposure to heat accelerates the degradation of polymers, leading to issues such as loss of gloss, yellowing, cracking, and reduced physical properties. This is where cool plastics come in. These are plastics that are designed to reflect heat, reducing the demand for interior building cooling and lowering air conditioning costs.
In certain applications, however, black plastic may be desirable due to its ability to absorb heat. For example, in a solar still, black plastic is used to absorb the sun's rays, heating up the air inside. This is also why black clothing is recommended for keeping the body warm in cold climates. Nevertheless, in hot climates, it is generally advisable to choose light-coloured clothing as it reflects heat better and keeps the body cooler.
While black plastic has its uses, it is important to be mindful of its heat-absorbing properties in certain applications. For instance, black plastic guttering can expand and contract in the sun, leading to mechanical distortion and leaks. Similarly, in a greenhouse, clear plastic is preferred over black as the aim is to let sunlight through to aid in the rising temperature and evaporation of water.
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IRR pigments reduce temperature
The colour of an object determines how much heat it absorbs and reflects. Dark colours absorb more light across the visible spectrum, while lighter colours reflect more light. However, this is not always the case, as two objects that appear identical in visible light can have different reflectance characteristics in the infrared (IR) range.
Infrared-reflective (IRR) pigments can manipulate the reflectivity of an object. IRR pigments can be used to create coatings and materials that meet infrared reflectivity and durability requirements, while also providing deep and rich colours. These IRR pigments can be used to formulate coatings that reflect IR radiation, which will remain significantly cooler than their IR-absorbing equivalents under the same environmental conditions. For example, the Shepherd Color Company's Arctic line of pigments provides a palette of colours that allows the formulation of coatings with high IR reflectivity.
IRR pigments can be used to reduce temperatures in buildings, vehicles, and clothing. For instance, using IRR pigments in exterior cladding and roofing materials can decrease the amount of heat conducted into a building, reducing the internal temperature and the need for air conditioning. IRR pigments can also be used in vehicle trim and clothing to keep them cooler in sunny conditions.
The use of IRR pigments can also extend the working life of plastic products. Heat accelerates the degradation of polymers, leading to issues such as loss of gloss, yellowing, cracking, and reduced physical properties. By lowering the service temperature through the use of IRR pigments, the demand on the heat stabilisation package in PVC is reduced, extending its working life.
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Light colours reflect heat
When sunlight hits an object, some of that light gets converted to heat. The more light an object absorbs, the more it heats up. Therefore, dark colours absorb more sunlight than lighter ones, which is why wearing black clothing on a hot day can make you feel even hotter.
Light colours, such as white, yellow, green, and silver, reflect the most solar heat, keeping surfaces cooler than darker colours. White reflects nearly all visible wavelengths of light equally, meaning that most sunlight bounces off the surface rather than being absorbed as heat. A white roof or exterior paint colour can lower indoor temperatures in hot weather.
Yellow reflects about 60% of sunlight, absorbing the remaining 40% as heat. Similarly, green reflects blue and red light but absorbs some light from the green to violet portion of the spectrum. Light colours like pastel yellow are perceived that way because most light wavelengths are reflected back to our eyes.
Glossy or shiny surfaces also reflect more light than matte or textured finishes, which absorb more. Shiny yellow will still absorb more heat than shiny deep blue. However, even darker colours can reflect most heat if they have a reflective sheen.
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Frequently asked questions
White plastic reflects heat the best.
White objects reflect nearly all visible wavelengths of light equally, while black objects absorb most of the light that hits them.
Yes, wearing light-colored clothing can help keep you cool in hot weather.
In addition to color, the finish of a surface can affect heat absorption. Glossy or shiny surfaces reflect more light, while matte or textured finishes absorb more.
Yes, using cool plastics in building construction can help reduce interior temperatures, lower the demand for air conditioning, and extend the working life of PVC products.
