Heglum

Heglum was a very light, synthetic gas used in dirigibles. Sometimes found inside of nebulae, it quickly bonded to a starship's sublight drives. Ships passing through heglum clouds need to undergo regular drive scrubbing inorder to remain at optimal performance.

Appearances

 * Darkstryder: Kathol Rift
 * Galaxy Guide 2: Yavin and Bespin

==Sources
 * The Complete Star Wars Encyclopedia