Technical Guide

What is an R-value?

With buildings, we refer to heat flow in a number of different ways. The most common reference is “R-value,” or resistance to heat flow. The higher the R-value of a material, the better it is at resisting heat gain (or heat loss).

What is the R-Value measurement units commonly used?

There are two commonly used units based on British Thermal units (BTUs) or, metric units given in Watts. As different values associated with different units, it is essential to verify which are the units used for a given R-value. For Example:

R 1 based on m2xºC/W is equal to R 5.677 based on hrxft2xºF/Btu

In cases where R-value is shown using m2xKºC/W, it can be treated as the above metric calculation (m2xºC/W) without further changes.

Conversion table:


What is a Total R-value, or system R-value (RT)?

The Total R-value (RT) is the total resistance of a building element such as a roof, wall, floor or ceiling. It takes into account resistance provided by each given construction material, internal air spaces, and the air film adjacent to solid materials. This allows architects and consultants to asses the overall thermal resistance of the complete component (such as roofing system).

What is U-value, or, U-factor?

U-factor (or “U-value,” as it is often called) is a measure of the flow of heat (Thermal transmittance) through a material, given a difference in temperature on either side. In other words, U-factor is the reciprocal of the Total R-value (1/R) of a given structure. It is referred to as the Overall Co-efficient of Heat Transfer.

Conversion Table:


Why we aim to promote Total R-value or system R-value (Rt)?

We all familiar with the “top floor phenomena” presents in multiple storey buildings, or, houses. In summer, top floors (under the roof) always hotter, and harder to cool down. Is that “God’s will” or just poor design? We can safely assume that it does relate to poor design…
In order to avoid being subjected to poor design, it is essential to evaluate the actual SYSTEM R-value. What will be the actual R-value achieved in a specific design, in a precise location, under particular climate conditions.
When using BULK insulation, architects and designers pay very little attention to the Total R-Value. They assume to meet R-Value requirements by “plug-in” the BULK insulation with manufacturer’s R-Value labels.
In a perfect world, with no moisture, at 12 ºC – 24ºC constant temperature, free labor and un-limited space between building elements, such R-Value could be obtained. But, in real life… well… it is a different story.
When using Polynum™ we provide an accurate R-Value analysis based on the real factors:

  • Section design (roof, wall, floor and so forth)
  • Actual location of Polynum™ per given design
  • Climate zone (temperature, moisture)
  • Effect of related building elements on Polynum™ performances

With Polynum™ Total R-value we don’t have to worry about cooling the top floors, anymore!

Thermal Conductivity

Thermal Conductivity depends on the substance (material) a given object is made of. Certain substances like metals pass heat very readily. That means when a metal molecule (atom) vibrates, its neighbors quickly begin to vibrate too. If a substance doesn’t pass heat well, it can be used as thermal insulation preventing heat conduction. The surface atoms (or molecules) vibrate, but nearby atoms aren’t as apt to start. Thermal conductivity determines by K value.

What is K-value?

Heat transferred by conduction is governed by the fundamental equation described by Fourier’s Law: (rate of heat flow) = k x (Area) x (Temperature Gradient):
The ability of an object to move heat from one part of itself to another is called “thermal conductivity”.
The higher the K value, the faster the development of heat in the object. The lower the K value per a given time/area, the better the resistance conduction heat transfer

Is K-value is relevant to Polynum™ Insulation?

Not so much. K-value refers to bulk insulation and has little relevancy to reflective insulation. K-value is needed to determine R-value of bulk insulation. Greater part of Polynum’s™ R-value is determined by emissivity and air cavities, and not by the material thermal conductivity. Just the R-value of Polynum’s ™ closed air cell structure (the inner core of Polynum™ insulation) determined by K-value. As most of Polynum’s™ closed air cell structure filled with air, the thermal conductivity or, the K-value is very low.

How does Polynum™ Insulation work?

Polynum™ Insulation consists of the physics of reflective air space combines with low K which is obtained by the closed air cell structure. Due to dual or more highly reflective foils (low emittance), Polynum™ Insulation’s reflects up to 97% of radiant heat away from its surface. Very small quantity of heat absorbed will be further reduced by Polynum™ low-K closed air cell structure.

Summer and winter R-values with Polynum™


Polynum™ Insulation is effective against radiation and conduction forms which are not much affected by heat flow direction (see table). As shown in the table, presences in winter, changing the heat flow balance. The movement of hot air upward direction, carried by natural and\or forced convection (The flow of heat energy through liquids and gases Hot air will rise, Cold air will sink. Hot room air is forced outside, while cooler air replaces it). Therefore, when calculating System R-value (Rt) considering a horizontal air spaces found in roof space or sub-floor space, the total R (Rt) will always have a higher resistance to heat flow in the downward direction (summer). Looking at the above table, we can see that convection heat transfer through walls is the same for winter and summer. There is no difference in system total R-value (Rt) for walls during summer and winter.

Heat transfer by movement of air. Convection is the circulation of hot or warm air. As the air heats up, it becomes less dense, and rises. Cool air is then forced down and warmed by the heat source in a continuous cycle, or convection loop. The stiller the air is, the less heat transfer occurs through convection. Polynum™ products are totally airtight and effectively seals out wind. Its internal composition – trapped dry air bubble film and layers of steady trapped dry air – considerably reduces convection. Same as conduction heat, convection heat is not possible in vacuum. The different of temperature between hot and cold area is described as thermal gradient.

Will your Polynum™ work as efficiently in winter as it does in summer?

Reflective Insulation will reduce heat gain (summer) and heat loss (in the winter), so it will benefit both winter and summer savings and comfort. In the summer, heat is reflected back to the outside and in the winter, heat is reflected inwards.

Why Polynum™ R value is given per system (Total R-value)?

Different applications will have different Total R-Values following the R-values of each of the building components such as tiles, metal roof, bricks, timber, as well as the installed circumstances of Polynum™ Insulation such as condition (for example ventilated or non-ventilated) and size of air spaces (cavities).

Installation and related issues

How do I install Polynum™ Insulation to my walls/ceiling/roof/under-floor, etc?

Polynum™ Insulation is easily installed using nails, screws, or a staple gun. For detailed installation instructions for a range of applications refer to the Installation guide

Why Polynum™ insulation requires air spaces when installed?

Polynum™ Insulation consists of the physics of reflective air spaces (cavities). An air space by itself does not provide much of thermal resistance. However when combining an air space with low emittance surface such as found in Polynum™ Insulation, it will have significant resistance to the heat transfer.

What is the optimum air-spaces recommended for Polynum™ insulation?

Generally, the bigger the air space, the better the performance of Polynum™ Insulation for heat flow down. It said that dual air spaces of 80mm to 90mm each would be enough to provide optimum R-value for downward heat flow, and 20mm for horizontal heat flow. Realizing the construction constraint to obtaining such dual generous air spaces specifically under roof we have developed products which maximize the system R-value, with less than optimum air spaces. For example, Polynum™ Ultra® compensates with an internal robust R-value. We need to keep in mind that although dual air spaces of 80 to 90mm are recommended to maximize total R-value, Polynum™ insulation can achieve high R-values with single air space, or, less than optimum air spaces!

Do I need to tape the joins?

In most Polynum™ Insulation applications you will need to tape the joins, some by overlapping by 50mm some by butt joining. In case where no taping is an option Polynum™ insulation is to be installed by overlapping by 150mm (the alternative is overlapping by 50mm and taping). For comprehensive details on overlapping and joining refer to the Polynum™ Installation guide

Does Polynum™ Insulation need support mesh?

No. Polynum™ is self supported product. Most Polynum™ products can be stretch upto 2.50m span without support.

Does Polynum™ require ventilation, and if so, what type (ridge, off-ridge, soffit, etc.)?

No, Polynum™ work with or without ventilation but will perform better in ventilated attics (in summer, or hot climate countries). According to the building code, in some countries all attics must be vented.

Can I install Polynum™ at a later time, after the house is completed?

Yes. Actual installation technique depends on the attic configuration, existence of bulk insulation and so forth. Kindly refers to Retrofits Installation Guides

Is Polynum™ Insulation affected by moisture?

No. Polynum™ Insulation is not affected by moisture. Polynum™ Insulation’s structure is entirely water resistant and can perform as a waterproof membrane and water vapor barrier. On top, Polynum™ Insulation’s pure aluminum foils are treated against possible corrosion (High Resistance Treatment).

Can I puncture Polynum™ Insulation?

Sometimes, during installation there is a need to puncture Polynum™ Insulation. Such puncturing will not have significant effect on Polynum™ Insulation thermal performances. Most of Polynum™ Insulation’s thermal resistance derived from the low emittance high reflective surfaces. Puncturing few closed cell air bubbles out of many others will not affect product integrity, and has no impact on the overall performances.

What are the conditions that will make condensation occur on the underside of an un-insulated metal roof deck or framing members?

Condensation will occur on any surface when the temperature of the surface is at or below the “dew-point temperature” for an air-water mixture. The dew-point temperature depends on the dry-bulb temperature (measured with an ordinary thermometer) and the relative humidity in the space next to the surface. The dew-point temperature is less than or equal to the dry-bulb temperature. The two temperatures are equal when the relative humidity is 100%. Some examples of dew-point temperature:


As you can see, condensation can occur when the outside temperature is cold. Insulation below a roof deck will have an inside surface temperature that is above the roof surface temperature. The actual temperature of the inside surface depends on the amount of thermal resistance between the roof and the inside surface. The higher the resistance, the closer the interior surface temperature will be to the inside air temperature. Maintaining a reasonable inside relative humidity (less than 60%) is an important factor in preventing condensation.

How will the addition of a Polynum™ with airspace between the roof deck and the aluminum surface change the conditions that cause condensation?

Polynum™ below the roof deck results in an interior surface temperature that is greater than the outside temperature (in cold weather). As the inside surface temperature increases, the conditions for condensation become less likely to occur.

Is a vapor retarder required as part of the solution?

A water vapor retarder is required. If interior air containing water vapor is allowed to come in contact with a cold roof deck, then condensation will likely occur. The insulation system that does not include a high quality water vapor retarder will be of little or no value in controlling condensation in cold weather.

Is Polynum™ acting as vapor barrier?

Yes, absolutely!!! All Polynum™ products are vapor barriers, meeting ASTM vapor standard requirements.

Products Information

What is Polynum™ Reflective Insulation and what is made from?

Polynum™ – a family of superior Thermal Reflective Insulation products designed for wide range of insulation applications, for both, summer and winter. Polynum™ a FIBER FREE PRODUCT constructed of pure aluminum foil (at least 99%) attached to polyethylene bubble sheeting in thermal process without GLUE or chemicals. Its unique design blocks 97% of the radiated heat (gain or loss), which penetrates (or escapes) a given structure or building.

Below 2 examples for Polynum™ products: Polynum™ Big made of 8mm bubbles, and Polynum™ Multi, which made of bubbles/xpe foam/bubbles.
All Polynum™ products carry minimum of 7 to 15 years warranty against delaminating and related manufacture defects.
Polynum™ products’ embodied energy (energy consumed in the manufacturing and distribution process) is low. Therefore Polynum™ is one of the quickest products to recover its embodied energy.

What is the difference between Polynum™ products?

Polynum™ products differ by their layers structures, layers formulations, nominal thickness, thermal and acoustic properties, and surface finish.

We have defined Polynum™ products per their basic structures or dedicated usages. Polynum™ products’ are divided into 7 categories:

  • Single bubbles: Polynum™ One, Super and Big
  • Double bubbles: Polynum™ Double
  • Multi layers: Polynum™ Multi, Ultra
  • Livestock: Polynum™ Premium family, Acid Proof products, Polynum™ Silver
  • Radiant barriers: Polynum™ LB
  • Floor solutions: Polynum™ anti impact family, Polynum™ CBF
  • Special products: Polynum™ Gold series, Polynum™ White, Polynum™ Black, Polynum™ Anti-Glare, Polynum™ Sound and Polynum™ Foam (PolyFoam)

Kindly refer to each product page for full product information and benefits.

What is the difference between “Polynum™ One” and “Polynum™ Advanced” (Polynum™ White)

Polynum™ one based on single external pure aluminum foil layer attached to flame retardant polyethylene bubbles. Polynum™ Advanced constructed with two external pure aluminum foil layers covering single core of polyethylene bubbles. One of the external pure aluminum foil layer is treated with special low Emissivity white coating.

What is Polynum™ Sound©?

Polynum™ Sound© is a family of reflective insulation products with outstanding acoustic properties, such as STC (Sound Transmission Coefficient). Polynum™ Sound© are available at 1kg/m2 and 2kg/m2 configurations.

What is Polynum™ Ultra©?

Polynum™ Ultra© is one of our patented products with extremely high R Value per nominal thickness. 16mm of multi reflective layers providing complete insulation solutions for both, summer and winter, for wide range of building applications.

Would using multiple layers of Polynum™ Insulation is providing better thermal resistance?

Multiplying Polynum™ Insulation layers can improve the overall system R-value (Rt). The overall benefits depend on the installation of the additional layers. Using proper air spaces between Polynum™ layers can improve system R-value significantly.

Why Polynum™ Multi Foils Products such as Polynum™ Ultra perform better than double-sided reflective insulation such as Super Polynum™?

Multi foils products have higher material R (the material R value without air spaces, or, the material K value. Additional foils embedded into the product reduce heat transfer between the bubbles, creating “internal reflective space”. For example, Ultra material R value is 0.45 m2xºC/W (R 2.55 hrxft2xºF/Btu) compare with R 0.10 (0.57) for Super Polynum™. In walls applications, the Ultra material R has significant effect on the total system R value (Rt) compare with Super Polynum™.

What is Polynum™ insulation fire rating?

Polynum™ Insulation is exported to more than 40 countries. Many of these countries require insulation materials to meet certain fire rating. Part as being a leader in the reflective insulation field, Polynum™ Insulation complying all major fire ratings such as: BS 476 part 6&7 (Class 1 and Class 0), ASTM, AS/NZ (1530.03, 1530.02), DIN, M1 (French and Spanish standards), new European standard, JIS (Japanese standard) and many more.

Where can I buy Polynum™ Insulation?

Polynum™ reflective insulation is available in more than 50 countries worldwide. Please refers to your country link or just, contact us directly for further information.