Polymer foaming provides material with a porous or cellular structure. In the foaming process, the polymer converts the material with a low dense (very little compared to non-foam plastics) with good energy absorption properties in a good thermal insulator.

Generally for foam polyethylene (XPE), polypropylene (XPP) or polystyrene (Exps), a nucleus filler is used in very few percent (not more than 1%). This filler enables the formation of air cells within the polymer matrix, which gives its fungi.