**3.1 Manufacturing techniques of open-pore foams**

Manufacturing techniques of open-pore foams can be classified into four groups attending to the state of the precursor material: liquid, solid, vapor, and ions [1].

**Liquid state processing**: the precursor material is in liquid state. The most important processing techniques are:

a.Investment casting with polymer foams

b.Casting around space holder materials/infiltration of martyr preforms

**Solid state processing**: the precursor material is in solid state. The following techniques are the most important ones:

a.Partial sintering of powders and fibers

b.Foaming of slurries

c.Pressurization and sintering of powders in martyr preform

d.Sintering of hollow spheres

e. Sintering of powders and binders

f. Reaction sintering of multicomponent systems
