What Is Foil Insulation?Foil Insulation or reflective foil insulation generally refers to products comprising of one or more substrates with a reflective foil backing one or both sides. The reflective facing is usually a very thin layer of reflective aluminium foil, hence the name reflective foil insulation.
History Of Reflective Foil Insulation
Reflective foil insulation is very simple and very effective but it’s not a new idea, and although reflective foil insulation was
The Beginning: Reflective insulations were used by ancient cultures, there is evidence to show that even the Egyptians would use polished metals to reflect heat out of homes.
1800’s Mass-market: The most popular and probably well-known example of using reflective surfaces and airspaces to insulate is probably down to the inventor Sir James Dewar who invented the thermos flask in 1892.
1900’s Re-popularised: Reflective foil insulation materials were
2000’s Well known uses – today: No doubt you have seen people running marathons and outdoor events. You will also have noticed competitors are often wrapped in foil blankets… but not fibrous insulation and not foam. Ever wondered why, or why we don’t
How does Insulation Work?
Most common insulation materials work by slowing heat flow. Radiant barriers and reflective insulation systems work by reducing radiant heat gain. For foil insulation to be most effective, the reflective surface should face an air space.
To understand how insulation works, it helps to understand the basics of heat flow, which involves three basic mechanisms — conduction, convection, and radiation.
Three Types Of Heat Loss
What Is Conduction?
Conduction is when heat travels between two touching objects or through one solid object.
What Is Convection?
Convection is a warm air current, you can see convective heat from a hairdryer or from the surface of a hot road.
What Is Radiation?
Radiant heat is electromagnetic waves which can pass through anything.
Heat flows from warmer objects, airspaces or surfaces to cooler ones, until there is no longer a temperature difference. In your home, this means that in winter, heat flows directly from all heated living spaces to adjacent unheated attics, garages, basements, and anywhere else that is cooler than your heated area. Heat flow can also move indirectly through ceilings, walls, and floors. The opposite is true in the summer, where heat is transferred from outside into your cooler home.
Why Do We Insulate?
Most people believe that we simply insulate to keep warm. In fact, we insulate for a number of reasons:
- Thermal Efficiency
- Air Tightness
- Condensation Control
- Energy Saving
Before we talk about foil insulation, we need to define three thermal values
What Are R-values?
R-values measure a material’s resistance to heat flow. The thermal properties of insulation products are commonly stated in R-values.
What Are U-values?
U-values are a measure of a material’s ability to conduct heat. The thermal performance of windows, doors and buildings is commonly stated in U-values. U-value is equal to 1/R (R-value).
What Are E-values?
E- Values are the measure of ‘emissivity’ which is the ability to emit or transfer radiant heat through a surface – everything has an E-value. The ‘E’ in Low-E stands for Emissivity.
Regardless of how high the R-value on an insulation product is unless it also has a low – E value it has no ability to reflect radiant energy. It will always need to absorb the heat in order to work.
Very high R-values don’t stop heat transfer, they simply slow it down. You cannot ignore the need for good R-values, but by addressing the R-value alone, a large percentage of heat transfer is being ignored.
What is Emissivity?You may have heard of low E glass in windows. Well the ‘E’ stands for Emissivity and Low-E Insulation works the same way.
“If a surface emittance is changed from .90 to .03 the part of the heat flow that is radiation is reduced to 3.3% of its initial value.” 100 Btu/hour – 3.3 Btu/hour
“Radiation is the primary mode of all heat transfer. The other two modes… come into play only as they interfere with the primary mode.”
M. Pelanne, Senior Research Specialist for Johns Manville (Energy Design Update, Feb. 93)
While there are all three forms of heat transfer out of a building, it is worth noting that 100% of the solar gain is radiant heat. Consider how hard air conditioner have to work during summer months to deal with that.
Why do Airspaces and R-values matter?
Reflective foil insulation products can work without
The easiest way of explaining how low emissivity airspaces work is to use a double glazed window as an example. The two pieces of glass on their own do nothing but when the layers of glass are separated by
Heat cannot conduct through