Prefab Building Technology

Q: What is the difference between a EPS and polyurethane panel?

A: Polyurethane (PU) is much more expensive than expanded polystyrene (EPS), and most suppliers in the panelised market use EPS due to the low cost and easy manufacturing. There are large differences between EPS and PU.

Thermal Insulation – PU is a much better thermal insulator than EPS and has approximately 1.5 times more insulation resistance than EPS. For example for a typical 40mm PU panel you will need a 63mm EPS panel to achieve the same thermal insulation (R  – Value).

Moisture Resistance – Water permeability can be an issue with buildings and cold rooms. When water enters the panel you can get rot or mildew, and moisture seeping through the wall and creating damp. PU has an excellent permeability rating due to the closed cell nature of the PU foam, with no voids between the cells. EPS has a closed cell structure but there are voids between the cells, and moisture can permeate more easily through EPS than PU. The additional effect of moisture in the wall panel is a dramatic loss of thermal insulation as moisture is an excellent conductor of heat/cold. Depending on how cold it gets the moisture in the panel can also freeze and create further structural issues.

Fire Resistance – Both EPS and PU will burn and most panel suppliers use a fire retardant in the EPS or PU, this ensures that when the flame/heat source is removed from the material both EPS and PU wall panels will self extinguish. Both PU and EPS emit noxious and asphyxiating fumes, but PU will emit a small percentage of hydrogen cyanides and chlorides which are toxic if inhaled directly.

As PU is a thermal-set material it will not melt in a fire/heated situation, and only above 1,000 degrees C will it char. EPS will soften at around 180 Degrees C and will melt at around 240 degrees C. This is why you can cut EPS with a hot wire, and that does not work with PU.
DENSITY – The density of a product will contribute to the strength. EPS has a density of 12-22 kg/cbm and PU has a density of 36-40kg/cbm.

CHEMICAL RESTANCE – PU is resistant to most counter chemicals. EPS react most solvents or petroleum based products.

MANUFACTURING – Probably the biggest difference between PU and EPS is in the manufacturing process of these panels. As PU and EPS are used as panel cores they need to the bonded to the steel/timber/fibre cement. As PU is one of the best adhesives available it has a very strong bond to the panel skin. EPS needs to be bonded to the panel skin and this process often creates voids in the adhesion layer and results in delamination of the panel skin.