The Qualities of a High Performance Heat Reflector

Heat reflectors are any material that reflects infrared radiation away from itself rather than absorbing and emitting it. You see this in daily life when you choose to sit on a white bench instead of a black bench on a sunny day. Technological and industrial insulation applications are sensitive to far finer temperature differentials than your rear end. A high-performance heat reflector must posses 5 qualities:

1. Low Emissivity

   Emissivity is a measure of how much heat a product emits: whatever percentage of heat a material doesn't reflect. Aluminum foil, for example, reflects 97% infrared radiation that hits it, absorbing and emitting just 3%. Compare this to white paint, which emits about 94% of the infrared radiation that hits it. Other materials used in high-performance insulation include gold (2.5% emissivity),  copper (2% emissivity), and silver (2% emissivity). The lower the emissivity, the less heat the material emits and more heat it reflects, and the better the insulation.

2. Corrosion Resistance

   Uncoated copper and aluminum film exposed to 100% relative humidityIron rust is just one form of corrosion, and corrosion of metals is a serious problem in heat reflection. As you can see in the photo, aluminum fades when it corrodes. That fading increases the aluminums emissivity, making it less effective as a heat reflector -- from 3% emissivity uncorroded to 60% emissivity or more. Sigma’s corrosion-resistant coating on all aluminum products has tested to prevent that corrosion even in high-humidity and high-heat environments. We also lead the industry in copper metalization, a trickier form of producing metallized fabric and film reflectors that is non-reactive with water.

3. Flame Resistance

   This is a safety and compliance factor rather than a reflectivity issue, but safety and compliance are part of the professional landscape in almost every industry. When tested via the ASTM E84 test (the material is laid horizontally with a flame underneath, and testers determine the amount of flame and smoke that develops), the two most common forms of high performance heat reflection perform differently:
   • Aluminum foil laminated to plastic resists the fire for a short time, then begins to burn. In many cases, this fails to pass building codes because it isn’t sufficiently flame resistant and can spread the fire
   • Metallized films begin to melt immediately, but seldom catch fire in this test method. As a result, these metalized film products are deemed safer by building codes.

   Which is better depends on the specific application of your heat reflector. The option that doesn’t burn is attractive because it won’t add fuel to a fire. However, some industrial sites have fire prevention systems where the resistance of aluminum foil would result in less damage during a fire, especially if the final product is laminated to something non-flammable, like fiberglass instead of plastic.

4. Pliability

   The degree to which a reflective surface can be shaped, sewn and draped is the degree to which it’s valuable in some settings. Truly high-performance low-e fabrics like those in tents, protective clothing and industrial heat curtains are hard to tell from those laminated to stiff aluminum foil. Developing a low-emissivity fabric that still behaves like a fabric is isn’t easy, because the usual methods, like laminating a film or even a metalized film, add to the stiffness. Sigma Technologies has a patented process of coating and metalizing a fabric directly to minimize the emissivity without affecting the breathability, sewability or drape of the fabric itself.

5. Insulation Values

   The insulation value of a layer of reflective material is a function of its emissivity, which we discussed above. However, high-performance reflectors are often paired with other kinds of insulation like fiberglass, foam or bubble-pack to increase the overall R-factor of the finished product. Also, a single sheet of film foil low-e fabric can be used alongside a separate insulator like fiberglass or foam. For example:
   • Reflectix's bubble-pack insulation consists of plastic air bubbles laminated to aluminum film, producing R-17 in about 5/16 inch
   • Prodex’s laminated foam insulates at R-16 with a 13/64 in layer of foam laminated to a thin layer of aluminum foil.
   Both products are easier to handle, quicker to install, and outperform simple 3.5 inch fiberglass batting. How important this factor is depends on the specifications of the finished product. In some cases, it’s not relevant. In others, it’s the difference between being a market leader and being an also-ran.