Flamethrower fuel canisters come in a variety of sizes, depending on the model of flamethrower they are designed to fit. The smallest fuel canisters, holding anything up to half a litre of fuel, are used covert operations flamethrowers, which are designed to be portable and concealable to a degree. The largest fuel canisters for portable flamethrowers, designed to be worn as part of a backpack mount, can contain up to twelve litres of fuel under high pressure.

Regardless of their size, fuel canisters are designed for a single purpose – to safely store highly combustible liquid compounds under high pressure. Fuel canisters are typically thick walled metal cylinders with a control/release valve at one end. Better manufactured canisters feature double walls, although this adds considerably to the weight. Indeed, the larger, backpack mounted flamethrower rigs can weigh upward of forty kilograms.

In the early years of projectile warfare, when solid slugs were the norm, the risk to flamethrower users was considerable. Should a metal bullet puncture the fuel canister and ignite the contained fuel, the wearer could expect a horrible death. Modern fuel canisters will usually be constructed with an ablative outer shell to attenuate the force and heat of blaster bolts, slightly increasing the safety of the wearer. Nevertheless, one should do as much as possible to avoid exposing fuel canisters to directed weapons fire, just to be safe.