Refer to figure.
AIRCRAFT FUEL TANKS

• INTEGRAL TANKS:

Integral Tanks are used on all modern large passenger aircraft and, as its name suggests, a tank is formed as an unit within the airframe structure by sealing part of the structure of the wings or fuselage with a fuel resistant two-part sealant. The sealed skin and structural members provide the highest volume of space available with the lowest weight => this is otherwise unused space inside the wings. Aircraft with integral fuel tanks in the wings are said to have wet wings.

• RIGID TANKS:

A rigid tank is a sealed metal container strapped into a compartment designed to accommodate the tank in the airframe structure. They are simple and may be removed for inspection, replacement, or repair. However, this type of tank adds extra weight.

• FLEXIBLE TANKS/FUEL BLADDERS:

Flexible tanks are reinforced rubberized bags installed in a section of the aircraft structure designed to accommodate the weight of the fuel. A bladder tank contains most of the features and components of a rigid tank but does not require as large an opening in the aircraft skin to install. It is rolled up and installed into the compartment through the fuel filler neck or access panel, and is secured by means of metal buttons or snaps inside the compartment. One major down-side to this type of tank is the tendency for materials to work harden through extensive use making them brittle causing cracks.