Board Thread:Questions and Answers/@comment-26932251-20160101213041/@comment-27441457-20160101232938

The main story always mentions that vertical maneuvering gear runs on gas.

The Before the Fall spinoffs go on to say that VM gear runs on gas that is formed from a substance called "iceburst stone", a substance that is solid at cold temperatures but rapidly sublimates into gas when exposed to room temperature, allowing for great amounts of gas to be yielded from small amounts of the solid stone. However, since this is spinoff material, the SNK Wikia considers this non-canon, so we can't be certain of how valid this is in the main storyline. Isayama may have his own system of how VM gear gas works. Or perhaps even if iceburst stones are canon, a new substance might have taken its place down the line in the same way (if BTF were considered canon) ultrahard steel would replace dwindling amounts of iron bamboo, another substance discussed in Before the Fall.