What is "R" Value?
The R value is a measure of Thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux (heat transfer per unit of time). Thermal resistance varies with temperature, but it is common practice in construction to treat it as a constant value.
How are 'R' Values established or Measured?
R - values are obtained using a formula that measures the ratio of temperature difference between two different sides of a material, and the amount of heat that can pass through it.
When an R - value is recorded for an insulation type, it is specifically measured against that material alone, without any additional layers or insulation specifics being taken into account.
R - Values in Australia conform to the International system of Units (SI - metric units), while those in the USA (based on imperial measurements - ie in Fahrenheit rather than Celsius) are approximately 5.71 times those using the SI measurement. It can be difficult to determine the difference between the US and SI measurements as R- Values are typically expressed without acknowledging which system it is based on. This is particularly apparent in the Window furnishing Industry where there has been no standard for rating the value added by a window furnishing product. Some are in Imperial and some in metric measurement and this confuses the consumer. The Blind Energy Rating Scheme (BERS) being implemented by the BMAA (Blind Manufacturer's Association of Australia (www.bmaa.net.au ) is seeking to address this issue and all products will then be assessed under the same criteria.
What does the R - Value have to do with Insulation?
The R - Value of a substance is its direct measure of resistance to transferring energy or heat. Generally R values are expressed using metric units m2.K/W . The higher the figure, the better it is at resisting energy transfer, so the easier it is to maintain a difference in temperatures across it for a longer time.