Foam Board Insulation: Extruded, Expanded Polystyrene Foam Board

Foam board insulation is used in a variety of forms and locations to insulate a structure. Extruded and expanded refer to the process of how the polystyrene foam board is created, often referred to as XEPS.

Molded Expanded Polystyrene

Polystyrene can also be molded. Shipping material and soda cups are just a few of the alternate items polystyrene can be molded into along with being molded into foam board insulation. Not quite as strong as XEPS, however, this is also an excellent choice for some insulation projects.


The process for manufacturing extruded, expanded polystyrene foam board is done by combining polystyrene crystals with additives that liquefy the crystals; this combination is then mixed with a blowing agent and put into an extruder. The polystyrene mixture is melted, which causes gas bubbles and forms a thick, syrupy liquid. This viscous liquid is directed to a board die. The liquid is poured into a die board and cooled. While cooling, the polystyrene mixture expands. The finished product is very strong due to its high compression strength. In some insulation situations this foam board adds structural strength.

Because of its resistance to moisture absorption, its strength and its R–value, extruded expanded polystyrene foam board insulation is an excellent choice for use as roofing and wall insulation.