Foams are artificially produced materials with cellular structure and low density.
- Closed-cell foam: the walls between the individual cells are completely closed
- Open-cell foam: the cell walls are not closed; these foams can therefore absorb liquids
- Mixed-cell foams contain both types of cells
- Integral foams: they have a closed, thick outer skin and a cellular core; the density decreases
towards the core
Foams are characterized by a very low density (weight per volume) and thermal conductivity with only low strength. Due to the interior structure, components made of foam are virtually free of residual stress.