Both from the substance called styrene, the expanded polystyrene (or expanded polystyrene) comes in the form of very light white foam, often molded into small balls that are in contact with water vapor at temperatures above 90 ° C and pentane, a gaseous hydrocarbon, their initial volume is expanded up to 15-45 times.

EPS (expanded polystyrene) is produced in sheets that can reach 4 meters, with a density of 25 kg / cubic meter.

The extruded XPS (extruded polystyrene foam) is more compact because its closed cell structure (extruded) is homogeneous and stable, which makes it impossible to absorb water and allows it a high resistance to compression. It is produced in very small sheets, often 1.5 meters long, with a density of 35 kg / cubic meter.

The performance evaluation of the two materials is based on:

• degree of air permeability

• degree of vapor permeability

• degree of water permeability.

EPS retains a certain permeability, even if lower than fibrous insulators; has a thermal conductivity λ = 0.035 W / mK and a resistance to the diffusion of water vapor μ = 50.

Used for coats, especially in horizontal interspaces, except for plinths where greater impermeability is required.

The XPS as previously mentioned is practically impermeable and has a thermal conductivity λ = 0.035 W / mK and a very high diffusion resistance of water vapor μ = 80-230.

Thanks to these characteristics, it is used more and more often in all the riskiest situations, including the skirting of the coats or in places directly in contact with the ground. Very often we can find it coupled with plasterboard or laminates in plastic and metal to isolate even floors, walls or ceilings.