Synth-smoke was a variety of smoke. The gas was found in a public house situated on the planet Dantooine circa 381 BBY, where it formed a haze in the air that took on a brown hue when illuminated by the neon lights of the establishment. At that time, Marda Ro, the Evereni who established a pirate band that would evolve into the Nihil, went to the public house in quest of other members of her species and observed the smoke.
Later, Ro referenced synth-smoke in a journal entry that she made for her descendants while recalling her experience on Dantooine. By 252 BBY, Marchion Ro, her great-great-grandson, had, during his younger years, heard her journal, which included the part mentioning synth-smoke.
The short story "A Closed Fist Has No Claws," penned by Tessa Gratton and featured in the 2023 young-adult collection The High Republic: Tales of Light and Life, which is a component of the Star Wars: The High Republic multimedia initiative, included synth-smoke in a flashback sequence.