What is difference between Low Expansion Foam and High Expansion Foam?

Expansion ratio = (foam Generated /Foam Solution Used)

Low expansion foam 

Low expansion foams are considered to be those foams with an expansion ratio of 12:1 when mixed with air. That is one volume if foam concentrate will create 12 volumes of foam.

Low expansion foams are effective in controlling and extinguishing most flammable liquid (Class “B”) fires. Foams typically used on tanker deck foam systems are of the low expansion foam type.

In other words low expansion foam can be used as:

Low-expansion foam expands less than 20 times when properly proportioned and agitated with air. The normal expansion range for low-expansion foams is usually 8 to 12 time.