A Canister is a small container created out of glass and puresteel. Inside, it is filled with magically perturbed essence. A canister can be broken, causing the essence inside it to climb out and alter the breaker, physically and psychologically. Usually, the effect of the canister is beneficial to the user due to the essence being modified for a certain change. They can be thought of as a mini-Geneforge; however they're less powerful than it but more specific. They are quite small and easily transportable, being small enough to fit several on a cart.
Presumably, the canisters were invented by Shaper Danette or her colleagues in Sucia Island, around the same time that the Geneforge was also invented. The mechanics of the canisters (the process in which the genetic code of the user is modified) seems to be similar. There are benefits to be earned from these.
The first canister used in the series upgraded the user's Firebolt spell. Other canisters increase other magic spells, while some increase the shaping skills of the user. Rarely, one would find a canister that upgrades a certain skill, such as Mechanics or Melee Weapons. The four basic skills even have corresponding canisters. The rebels favor canisters as they allow strong abilities to be learned in just a few moments whereas learning it would take years to perfect. In Geneforge 5, probably due to the advances of canister creation by the rebels, canisters can upgrade an ability twice.
An overlying theme of the use of canisters is the side-effects of them. This comes in the form of psychological changes, such as arrogance, uncontrollable anger and megalomania. Pale, cracked, itchy and glowing skin has also been described. These traits are analogous to those in the intelligent, shaping creations.
By Shaper law, canisters are illegal; the reason being that knowledge and power must be gained through deeds, not shaped purposely. In almost every Geneforge game, players that excessively use the canisters are given exception by Shapers not to be killed, unless it is a game ending. With the exception of Geneforge 1 and Geneforge 5, endings usually change depending upon whether the player uses only a few canisters or uses many of them. In Geneforge 1, the game assumes that the character will use canisters and the ending refers to their excessive use even if the player finishes the game without using any of them.