In the original series, the fumarello was a fairly large cigar, similar to a [[Wikipedia:parejo|parejo. Typically seen near or in Starbuck's mouth, much to the dismay of the Cylons and their chest armor (Lost Planet of the Gods, Part II).
In the re-imagining, the fumarello is much the same (mini-series), and is likely made from fumarella leaf. (Water)