How Does Reflective Foil Insulation Work?

The unique design of Low-E Insulation allows it to resist all 3 forms of heat loss and provide maximum thermal performance while also resisting moisture absorption, stopping draughts and uncontrolled air movement, and deadening sound.

Low-E is a very simple, very effective insulation material. It just so happens that is it also easy to work with, made from recycled material, safe to handle, has no airborne fibres to worry about, is Class 1 fire rated and can be used virtually anywhere!


History of reflective insulation

Reflective insulation is very simple and very effective but it’s not a new idea, and although reflective insulation was re-popularised by the space industry, it is not ‘space aged’ either. In-fact reflective insulation has been around for 1000’s of years.

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 know 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 Insulation where re-popularised by the space industry. Scientists were looking for a way of insulating space suits, and equipment to deal with the extreme heat and cold experienced by astronauts and shuttles.

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 utilise this foil technology in our homes and buildings?

How does Low-E Insulation work?

The unique composition of Low-E Insulation means that it can successfully tackle all three forms of heat loss. Low-E Insulation is made from pure aluminium which reflects 97% of radiant heat away from the surface and back to the heat source, while our recycled closed cell foam provides a tangible thermal break to reduce and stop conduction and convection

The first Question you need to ask yourself is; Why do we insulate?

Most people believe that we simply insulate to keep warm. In fact, we insulate for a number of reasons.

  • Comfort
  • Thermal Efficiency
  • Air Tightness
  • Condensation Control
  • Energy Savin

Before we talk about Insulation, we need to define three thermal values


R-values measure a material’s resistance to heat flow. The thermal properties of insulation products are commonly stated in R-values.



U-values are a measure of a materials 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).



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.

Three Types Of Heat Loss


Conduction is when heat travels between two touching objects or through one solid object.


Convection is a warm air current, you can see convective heat from a hairdryer or from the surface of a hot road.


Radiant heat is electromagnetic waves which can pass through anything.

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 U values, but by addressing the U values 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



Emissivity is the ability to transmit or transfer radiant heat through the surface of a material. Everything has an emissivity value. Clothing, wood, concrete. Cast iron has an Emissivity of .85. That means that 85% of the heat that comes in contact with its surface to pass through it, that is why traditionally radiators were made from cast iron. They were very efficient at transferring heat from one side to the other. Aluminium has a very low natural emissivity value of 0.03

Here are the emissivity values for a list of building materials

















Aluminium has a very low natural emissivity value of 0.03. This means that aluminium will only allow 3% of the radiant heat that comes in contact with the surface of aluminium will pass through it. Another way to look at this is that 97% of heat will be reflected back to the source.

“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

David Yarbrough

“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)

ALSO, SEE – [Aluminium -v- Mylar]

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 U values but by addressing the U values alone, a large percentage of heat transfer is being ignored.

Maybe we should ask the question; Why is so much importance put on ‘U’ & ‘R’ values?


Low-E Insulation is manufactured using 99.4% Pure “Insulation Grade” Aluminium which reflect 97% radiant heat. This has a massive impact on heat transfer into and out of a building. 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?

Foil insulation products can work without an airspace but to declare what is called an “R-value”, you must install foil insulation with an airspace. Airspaces can be forms in numerous ways and can be as small as a couple of millimetres but airspaces beside a low emissivity surface are most efficient between 6mm – 20mm.

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 an airspace, it is actually the airspace that becomes efficient. However, if there is a low emissivity surface (pure aluminium) on one side of the airspace, the airspace becomes nearly 5 times more efficient than in a double-glazed window.


Heat cannot conduct through a low emissivity airspace, and small airspaces are too restrictive for convection to occur. The Pure Aluminium surface of Low-E surface reflects heat into an airspace and the airspace becomes VERY efficient. Now you have an insulation system that can reflect all 3 form of heat loss.

We recommend installing Low-E Insulation with 2 airspaces whenever possible. Because Low-E utilises airspaces, the R-value for Low-E Insulation actually changes depending on the size of the airspace and the direction it is facing (horizontal or vertical).  Our technical team can easily calculate the R-value of Low-E Insulation in any application.

ALSO, SEE [Technical Support] 


Why is Moisture Control a problem?

Warm air carries more moisture than cold air. When warm air cools, the moisture gets left behind. To optimise performance in both new build and refurbished buildings, it is always advisable to install a vapour control layer within a modern building envelope.

Warm air carries more moisture than cold air. This is a problem for traditional insulation. When warm air cools down, the moisture from the air is left behind. It is then absorbed by the insulation causing the insulation to become compressed. This happens more so in winter when there is a greater difference between inside and outside temperature. Once this happens, the insulation’s ability to perform drops dramatically. In extreme cases, the insulation must be removed.

This can also be a problem if using single layered products. If warm and cold air spaces are separated by a single-layered product or a radiant barrier without a core, there is a greater risk of condensation forming within the insulation system. Standard breather membranes don’t have this problem because they don’t contain any metalized particles. Care should be taken to ensure this risk is dealt with through other methods of environmental control.


Our closed cell foam core provides a thermal break between the warm and cold surfaces, dramatically reducing the risk of interstitial condensation. Condensation will not form within the core and can’t travel through the product. The unique Low-E design allows it to self-seal around any nails or screws that puncture it during installation. Moisture problems are virtually eliminated.

Low-E® Insulation ’EZY’ Seal is a complete vapour control layer (VCL). It can be used to the internal side of a building envelope or structure.  Team Low-E Insulation with any secondary insulation and protect it from moisture absorption, extending the life of your insulation system. Low-E®’EZY’ Seal Insulation has been tested (BS EN 3177) and shown to have an MVTR rate of >2000 MN s/g

Low-E® Insulation PERF is a breathable reflective insulation. It has been designed to allow vapour transmission to pass through the material. It is ideally suited for use on the external side of an insulation system or in refurbishment projects, where it is necessary to maintain breathability.  Low-E® Insulation PERF has been tested to BS 3177 and shown to have an MVTR rate of 0.11 MN s/g making it suitable for use in both roof and wall systems.


How important is Air Tightness?

It is now widely accepted that air-tightness is one of the most important parts of building design and there is little point in improving insulation standards unless also addressing the levels of uncontrolled air movement.

The first thing to remember is that there is a big difference between breathability and air leakage. Air leakage is the uncontrolled movement of air in to and out of a building which is not for the specific and planned purpose of exhausting stale air or bringing in fresh air. Studies have shown that uncontrolled air leakage can account for over 50% of energy consumption within a building. So whether you are building a Passive House or upgrading an older building, air-tightness is now regarded as one of the most important parts of the design.

Air leakage should never be considered as acceptable natural ventilation because it cannot be controlled or filtered and will not provide adequate or evenly-distributed ventilation. It is generally at its most severe during the colder, windier, winter months and has least impact during the warmer, calmer, summer periods. This is generally the opposite of the requirements for ventilation within buildings. Ventilation of a building should rely on a designed strategy based on the assumption that the envelope will be relatively airtight.


Low-E Insulation eliminates draughts and uncontrolled air movement has. The pure aluminium foil is a completely airtight but foil on its own is not enough. Own closed cell foam provides a separating layer between the layers of foil and it is also airtight.

Why use an infiltration barrier that offers no thermal performance? Install Low-E Insulation in one labour step and gain a boost in thermal performance as well as addressing airtightness. Low-E Insulation was independently tested by the BBA (BS EN 12114) and shown to have ZERO Air-Leakage @ 600 Pa (m³ hr m)


It can be installed on its own or teamed with a secondary insulation to meet higher R-value standards. It is not meant to replace ALL insulations on the market. Low-E Insulation is designed to, increase thermal performance and airtightness, reduce condensation risks and life-cycle running costs, and most importantly, to tackle issues which have been previously unaddressed by traditional bulkier insulation products.

ALSO, SEE – [How is Low-E Made]

ALSO, SEE – [Low-E -v- Multi Foil]

ALSO, SEE – [Aluminium -v- Mylar]

How Does It Work?

Learn how reflective insulation works

Why Choose Low-E?

The worlds favourite reflective insulation

Where To Buy Low-E?

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