Doozer sticks are the thin, transparent modules produced by Doozers for use in their various construction projects. Building is what Doozers love to do, so they do it all day long. As such, the amount of space they are allotted to build in would be overrun were it not for the Fraggles' propensity to consume them as snacks.
It was revealed in the first season episode, "The Great Radish Famine," that Doozer sticks are made from ground-up radishes. This was a deliberate design feature by the Doozers, as radishes are the Fraggles' main food source. The Fraggles, however, would not realize this until season five's "The Gorg Who Would Be King." It is also suggested that the Doozers add flavoring to the sticks so the Fraggles find them tastier, as shown in "The Doozer Contest."
When the main Fraggle food source in the past was mushrooms, ("Born to Wander") that was also what Doozer sticks were made of. ("The Cavern of Lost Dreams")
When reintroduced in Fraggle Rock: Back to the Rock, the design had mostly changed from long thin sticks to hexagonal-defined grids.