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Expanded Polystyrene (EPS)

Expanded Polystyrene, or EPS for short, is a lightweight, rigid, plastic foam insulation material produced from solid beads of polystyrene (with a diameter of 0,2 to 0,3 mm). Expansion is achieved by virtue of small amounts of pentane gas dissolved into the polystyrene base material during production. The gas expands under the action of heat, applied as steam, to form perfectly closed cells of EPS. These cells occupy up to 50 times the volume of the original polystyrene bead. The EPS beads are then moulded into appropriate forms suited to their application.

There are 5 manufacturing stages:

  1. Pre-expansion: polystyrene granules are expanded by free exposure to steam to form larger beads, each consisting of a series of non-interconnecting cells.
  2. Conditioning: after expansion, the beads still contain small quantities of both condensed steam and pentane gas. As they cool, air gradually diffuses into the pores, replacing, in part, the other components.
  3. Moulding: the beads are moulded to form boards, blocks or customised products. The mould serves to shape and retain the pre-foam, and steam is again used to promote expansion. During moulding, the steam causes fusion of each bead to its neighbours, thus forming a homogeneous product.
  4. Shaping: following a short cooling period, the moulded block is removed from the machine, and after further conditioning, may be cut or shaped as required using hot wire elements or other appropriate techniques.
  5. Post-production processing: the finished product can be laminated with foils, plastics, roofing felt, fibreboard or other facings such as roof or wall cladding material.

Expanded polystyrene foam (EPS) is usually white. Some new innovative EPS products are grey due to the inclusion of graphite, which substantially increases the insulation performance. EPS is safe, non-toxic and inert. At any time of his life cycle does it contain any Chlorofluorocarbons (CFCs) or Hydrofluorocarbons (HCFCs).

The most important properties of EPS are :

  • excellent thermal performance (lambda between 0.038 and 0.030W/m.K)
  • high compressive strength
  • outstanding impact absorption
  • low weight
  • imperviousness to moisture
  • 100% recyclable

Extruded polystyrene (XPS)

Extruded polystyrene is produced by a continuous extrusion process: blowing-agent-free polystyrene granules are melted in an extruder and a blowing agent is injected into the extruder under high pressure where it dissolves into the polystyrene melt. This blowing-agent containing melt exits the extruder via a slot die. The blowing agent expands due to the drop in pressure which causes the polystyrene to foam into the form of a board with homogeneous and closed cell structure. The main used blowing agent is CO2. For some special applications requiring a very low thermal conductivity HFC’s are the preferred blowing agent. The blowing agents used for the products distributed by Saint-Gobain isover have zero ozone depletion potential (ODP).

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Variations in the slot die allow board thicknesses between 20 mm and 200 mm. After passing through a cooling zone, the boards’ edges are trimmed. The variation of process parameters during production allows the modification of the XPS product characteristics in order to satisfy the various application requirements. With foam densities between 20 and 50 kg/m3 compressive strength values can be achieved from 150 to 700 kPa. This corresponds to loading capacities between 15 and 70 tons per square metre. XPS’s rated thermal conductivity values currently range from 0.029 to 0.045 W/(m K). The closed cell structure of the XPS foam makes capillary water absorption impossible. But water vapour movement is possible through XPS foam.

Saint-Gobain Isover is not a producer of XPS: we distribute products manufactured by major XPS producers (BASF, DOW Chemicals…)