Foam is one of the herbal candidates for microwave treatment. The producing technique includes large drying and homogeneous consistency and microwave transparency makes drying with microwaves very efficient. [1]

Foams have been used in many applications because they have lower weight and high damping than solid materials. They are prepared by way of different methods such as extrusion, baking in a hot mold, compression molding, and freeze drying. The production of foams can be described in three steps; nucleation, bubble growth, and bubble stabilization.

Foams are often prepared from corn and potato starch. A microwave oven is a very fast way of adding heat and is usually used to heat foods containing starch. Because microwaving is a short and high energy dense process, it is a good way to create a thermoplastic material and foam starch. In an experiment, water-starch distribution heated by a microwave oven and foam produced. Firstly, the starch and deionized ultrafiltered water were mixed to distribute in the Teflon beaker. Then baker put in the microwave oven and heated for 3 minutes. A white distribution occurs when water and starch are mixed. When water starts to boil, starch is gelatinized. Then granules get swell. The steam bubbles created by means of the boiling water come to be trapped in the paste, for this reason increasing the paste. subsequently, the water evaporates and leaves a porous structure.

There is another experiment that prepares foams from different potato starch in varying quantities of amylose content, and water by using microwave technique. An improved concentration of starch in the preliminary water dispersion resulted in a much less dense foam shape. The potato amylopectin shaped open cell foams, while improved amylose content, as in local potato starch, yielded a more compact shape with irregular pore shapes. The high amylose potato starch yielded a shape with hardly ever any porosity. These experiments have shown that the molecular structure of starch polymers is more important than the starch polymer organization in granules in foam formation. [2]

Different types of foams are used for heat insulation in various industries. To be a good thermal insulator, low density, low heat conductivity, and low flammability are necessary. Using microwave and air to develope the resole-type phenolic foams brings low thermal conductivity and low density to the material that is insulation foams. [3]

Another example area of use for foams is dampening. Elastic foam base of polyurethane is used for dampening sound in automobiles. There are many conditions for foams for damping the sound within the engine compartment such as good acoustic sound, enough elasticity, low bulk weight, good mechanical strength etc. İt is hard to gratify all these conditions at the same time. Best way to satisfy these conditions is using microwave heating process for foaming. [4]

According to all experiments and above discussion, it is obvious that using microwave heating process while producing any type of foam is a better option than conventional processing methods due to many reasons.