Expanded Polystyrene (EPS) is a closed cell, rigid foam plastic used in insulation and packaging products. Since EPS is a closed cell structure, aging has no effect on the long-term thermal resistance. A common application of EPS in today’s society is the foam coffee cup, which effectively protects your hand from the hot or cold liquid within.
The manufacturing of EPS does not involve the use of ozone depleting CFCs or HCFCs. EPS starts off as small resin beads, having the consistency of table salt. These beads are expanded on the order of 50 times their original size in a pre-expansion process using steam and agitation. The pre-expanded resin beads are then dried, and aged for up to 48 hours to allow the pressure within the beads to equalize, and air to fill the millions of void spaces.
Once the aging process is completed, the expanded beads are molded into blocks, and then cut to the desired product thickness. The finished EPS is approximately 90% air. It is rigid, moisture resistant, has a low thermal conductivity, and can be cut into sheets or slabs to meet specific design reqiurements.
THERMAL RESISTANCE: A material’s ability to resist heat flow via the three heat transfer mechanisms: Conduction (measured as R-Value), Convection, and Radiation
IMPACT: Most Insulation Systems only consider conductive heat losses when evaluating insulation performance (R Value). Radiative and convective losses can amount to as much as 85% of a building envelope’s heat loss/gain(1)
Insulation is designed to effectively reduce the rate of heat loss (winter) and heat gain (summer) through a building envelope. Heat transfer can occur by the the following three mechanisms:
CONDUCTION: Transfer of energy from hot to cold regions of a substance by molecular interaction (direct contact). Measured as “R Value” in insulating systems.
CONVECTION: The conveying of heat through a liquid or gas by motion of its parts. It is conduction in a fluid as enhanced by the motion of the fluid.
IMPACT: Convective losses can account for up to 35% of a building envelope’s overall heat losses(1)
RADIATION: Tansfer of thermal energy in the form of electromagnetic waves travelling at the speed of light.
IMPACT: Radiative losses can account for up to 55% of a building envelope’s overall heat losses (1)
The process of heat transfer is a very complex topic, which is often oversimplified so as to help the consumer understand and make good insulation purchases. The problem is that oversimplification (such as using the R-Value system alone) can lead to errors in energy calculations and may result in a building being under or over-insulated.
As such, the amount that each heat transfer mechanism contributes to the overall heat loss from a structure will depend on the configuration of the building envelope, as well as other environmental factors, including but not limited to air infiltration, moisture, and extreme temperatures.
(1) CBD-149 “Thermal Resistance of Building Insulation”, Canadian Building Digest, NRC
The overall performance of an insulator must take into consideration real world factors such as installed performance, degradation, and how the product behaves as part of a building’s wall, floor or ceiling system.
When taking into account which parameters to consider when choosing an insulation, it is important to focus on the major issues associated with insulation and the thermal comfort, safety, and overall experience with the products. A list of key parameters is provided below:
- The Three Heat Transfer Modes
- Air & Moisture Infiltration
- Thermal Bridging
- Water Absorption
- Aging or “Thermal Drift”
- Physical Stability
- Installation Deficiencies
- Health & Safety
- Qualitative Comparisons
- Extreme Temperatures
Each parameter will have a varying level of impact on the building envelope’s ability to resist heat loss/gain.