**2. Types of foam**

According to the structure, a foam may be distinguished in two main types [2, 3]:

### **2.1 Spherical foam**

We can say it as a provisional dilute dispersion of bubbles in the liquid. It involves of gas bubbles separated by thick films of viscous liquid formed in recently prepared systems.

### **2.2 Polyhedral gas cells**

In polyhedral gas cells thin flat "walls" are produced on ageing with connection points at plateau borders [2].

Mainly, the spume can be categorised as:
