Propellants

Single base propellants include compositions that are principally gelatinized nitrocellulose and contain no high-explosive ingredient such as nitroglycerin.
Double-base propellants are mainly compositions that are predominately nitrocellulose and nitroglycerin.

Composite propellants are compositions that contain mixtures of fuel and inorganic oxidants but do not contain a significant amount of nitrocellulose or nitroglycerin.

There are also combinations of composite and double-base propellants.

Propellants are also classed by the way the grains of the propellant burn:

A propellant is said to be degressive burning when the surface area of the grains decrease as they burn.

An example of a neutral burning grain is a single perforated grain whose inner surface and its outer surface decreases as it burns. The result of these two actions is that the total surface remains the same.

As a multiperforated grain burns, its total burning area increases, since it burns from the inside at the same time. Thus, it is called progressive burning.

There are many different types of propellants currently in use. Some of the more frequently used types are black powder and smokeless powder.  Terrorists may use primer cord or TATP, a less expensive and fairly easily manufactured primer cord equivalent that can be manufactured in from relatively benign and easily obtained chemicals.